Method of manufacturing lithographic printing plate support

ABSTRACT

Disclosed is a method of manufacturing a lithographic printing plate support, including a step of subjecting an aluminum plate to at least: a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R a  is 0.25 μm or more but less than 0.40 μm, and an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R a  is 0.40 to 0.55 μm, with the treatments being performed in this order, so as to obtain a lithographic printing plate support. By this method, a lithographic printing plate support which can be used for a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate is obtained.

The entire contents of the documents cited in this specification are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a lithographic printing plate support. More specifically, the invention relates to a method of manufacturing a lithographic printing plate support used for a presensitized plate which has both an excellent scumming resistance and a good press life.

An aluminum support for lithographic printing plates used for a lithographic printing plate (hereinafter referred to simply as “a lithographic printing plate support”) is manufactured by subjecting an aluminum plate to graining treatment and other surface treatments. Examples of a known graining treatment include mechanical graining treatment, electrochemical graining treatment (hereinafter also referred to simply as “electrolytic graining treatment”), chemical graining treatment (chemical etching), and a combination thereof.

Among others, mechanical graining treatment is effective for the improvement of lithographic printing plates in press life. In a method for mechanical graining treatment which is generally known, a slurry of an abrasive is sprayed between a rotating nylon brush and an aluminum plate. It is also known to combine an electrolytic graining treatment with a mechanical graining treatment using a nylon brush and an abrasive (see, for instance, JP 2001-1663 A (the term “JP XXXX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”)).

JP 2001-1663 A proposes “a method of manufacturing an aluminum support for lithographic printing plate, comprising steps of mechanically graining an aluminum plate; subjecting the ground plate to alkali etching, and then to electrolytic etching in which a three-phase alternating current is used to carry out etching in an electrolyte containing 25 to 90 g/L of hydrochloric acid, 50 to 240 g/L of nitric acid, and 25 to 60 g/L of aluminum ions, with the hydrochloric acid and the nitric acid being present in the electrolyte in amounts of 1 to 1.5 parts by weight and 2 to 4 parts by weight with respect to one part by weight of aluminum ions, respectively; and subjecting the etched plate to desmutting, and subsequent anodizing treatment”. It is described in Examples of the published patent that “an aluminum plate in web form having a thickness of 0.24 mm is alkali degreased and then mechanically ground using a nylon brush rotating at a revolution number of 250 rpm and an abrasive chiefly composed of alumina and silica”.

The above method using a nylon brush and an abrasive has indeed the advantage of being performed at a high speed and low cost. In the method, however, it is difficult to control the particle size of the abrasive and mixed abrasive particles with large sizes are liable to form deep recesses locally. If deep recesses are locally formed on the surface of a lithographic printing plate support, some problems will arise. Specifically: The presensitized plate obtained by providing a positive-type image recording layer on such a support is hard to be developed in deeply recessed local portions of the non-image area. In the case of the presensitized plate with a negative-type image recording layer, its image formability is limited in deeply recessed local portions of the image area.

In other words, the presensitized plate using a support obtained by the manufacturing method of JP 2001-1663 A is inferior in developability (sensitivity) and scumming resistance as well, even though excellent in press life. A presensitized plate which fully meets the users' requirements is still awaited.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of manufacturing a lithographic printing plate support by subjecting an aluminum plate to a mechanical graining treatment with a brush and a slurry containing an abrasive and an electrolytic graining treatment, which makes it possible to obtain a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate.

In order to achieve the above and other objects, the present inventors have intensively studied to finally find out that the rate of deep recess formation in a mechanical graining treatment with a nylon brush and an abrasive is higher as the average surface roughness (R_(a)) is increased. To be more specific: If the average surface roughness R_(a) after mechanical graining treatment (for instance, mechanical grinding using a nylon brush rotating at a revolution number of 250 rpm and an abrasive chiefly composed of alumina and silica as described in Examples of JP 2001-1663 A) is large (e.g., 0.45 μm), many deep recesses are recognized on the treated surface of an aluminum plate. If the average surface roughness R_(a) after mechanical graining treatment is small (e.g., 0.30 μm), almost no deep recesses are recognized on the treated surface of an aluminum plate even if the average surface roughness R_(a) is increased (to 0.45 μm, for instance) by a subsequent electrolytic graining treatment.

Based on the findings as above, the present inventors have found that a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate can be obtained by using a lithographic printing plate support which is manufactured by subjecting an aluminum plate to at least a mechanical graining treatment which uses a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, and an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm, with the treatments being performed in this order. The present invention has been thus accomplished.

It has been found in particular that a presensitized plate will have a higher sensitivity as well as a higher scumming resistance, a better press life and further an excellent cleaner resistance when made into a lithographic printing plate, if it is obtained by using a lithographic printing plate support which is manufactured by subjecting an aluminum plate to at least a mechanical graining treatment which uses a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, an etching treatment in an aqueous alkali solution (hereinafter also referred to simply as “alkali etching treatment”), an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm, an alkali etching treatment, an electrochemical graining treatment in an aqueous solution containing hydrochloric acid, an alkali etching treatment, and an anodizing treatment, with the treatments being performed in this order.

Accordingly, the present invention provides the followings (1) to (3).

(1) A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least:

-   -   a mechanical graining treatment using a brush and a slurry         containing an abrasive to carry out mechanical graining such         that the average surface roughness R_(a) is 0.25 μm or more but         less than 0.40 μm, and     -   an electrochemical graining treatment for carrying out         electrochemical graining in an aqueous solution containing         hydrochloric acid such that the average surface roughness R_(a)         is 0.40 to 0.55 μm (first hydrochloric acid electrolysis), with         the treatments being performed in this order, so as to obtain a         lithographic printing plate support.

(2) A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least:

-   -   a mechanical graining treatment using a brush and a slurry         containing an abrasive to carry out mechanical graining such         that the average surface roughness R_(a) is 0.25 μm or more but         less than 0.40 μm,     -   an first etching treatment in an aqueous alkali solution (first         alkali etching treatment),     -   an electrochemical graining treatment for carrying out         electrochemical graining in an aqueous solution containing         hydrochloric acid such that the average surface roughness R_(a)         is 0.40 to 0.55 μm (first hydrochloric acid electrolysis),     -   an second etching treatment in an aqueous alkali solution         (second alkali etching treatment),     -   an electrochemical graining treatment in an aqueous solution         containing hydrochloric acid (second hydrochloric acid         electrolysis),     -   an third etching treatment in an aqueous alkali solution (third         alkali etching treatment), and     -   an anodizing treatment, with the treatments being performed in         this order, so as to obtain a lithographic printing plate         support.

(3) The method of manufacturing a lithographic printing plate support according to the above (2), wherein a desmutting treatment is performed subsequent to at least one of the first etching treatment in an aqueous alkali solution, the second etching treatment in an aqueous alkali solution and the third etching treatment in an aqueous alkali solution.

According to the present invention, a method can be provided of manufacturing a lithographic printing plate support allowing a presensitized plate of high sensitivity which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate, as will be described below. In addition, the energy required for the first hydrochloric acid electrolysis can be reduced by performing a specified mechanical graining treatment using a brush and a slurry containing an abrasive. The present invention is thus very useful.

Above all, the alkali etching treatments and the second hydrochloric acid electrolysis can provide a presensitized plate which has a higher sensitivity as well as a higher scumming resistance, a better press life and further an excellent cleaner resistance when made into a lithographic printing plate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a side view conceptually showing processes of brush graining in the method of manufacturing a lithographic printing plate support according to the present invention;

FIG. 2 is a schematic cross-sectional view of an apparatus for rinsing with a free-falling curtain of water that is used for rinsing in the method of manufacturing a lithographic printing plate support according to the present invention;

FIG. 3 is a graph showing an example of an alternating current waveform that is used in electrochemical graining treatment in the method of manufacturing a lithographic printing plate support according to the present invention;

FIG. 4 is a schematic view of a radial electrolytic cell that is used to carry out electrochemical graining treatment with alternating current in the method of manufacturing a lithographic printing plate support according to the present invention;

FIG. 5 is a schematic view of an anodizing apparatus that is used in anodizing treatment in the method of manufacturing a lithographic printing plate support according to the present invention;

FIG. 6A is a graph showing the sinusoidal waveform generated during the first or second hydrochloric acid electrolysis in Examples; and

FIG. 6B is a graph showing the trapezoidal waveform generated during the second hydrochloric acid electrolysis in Examples.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below in detail.

[Method of Manufacturing Lithographic Printing Plate Support]

<Aluminum Plate (Rolled Aluminum)>

A known aluminum plate can be used to obtain the lithographic printing plate support of the present invention. The aluminum plate used in the present invention is made of a dimensionally stable metal composed primarily of aluminum; that is, aluminum or aluminum alloy. Aside from plates of pure aluminum, alloy plates composed primarily of aluminum and containing small amounts of other elements can also be used.

In the present specification, various plates made of such aluminum or aluminum alloy as above are referred to generically as “aluminum plate.” Other elements which may be present in the aluminum alloy include silicon, iron, copper, manganese, magnesium, chromium, zinc, bismuth, nickel and titanium. The content of other elements in the alloy is not more than 10 wt %.

Aluminum plates that are suitable for use in the present invention are not specified here as to composition, but include plates of known materials that appear in the 4^(th) edition of Aluminum Handbook published in 1990 by the Light Metal Association (Japan), such as aluminum alloys bearing the designations JIS A1050, JIS A1100, JIS A1070, JIS A3004 and International Alloy Designation 3103A, with the last two materials being manganese-containing aluminum-manganese-based aluminum alloys. For increased tensile strength, it is preferable to use aluminum-magnesium alloys and aluminum-manganese-magnesium alloys (e.g. JIS A3005) composed of the above aluminum alloys to which at least 0.1 wt % of magnesium has been added. Aluminum-zirconium alloys and aluminum-silicon alloys which contain zirconium and silicon, respectively, may also be used. Use can also be made of aluminum-magnesium-silicon alloys.

An aluminum plate obtained by rolling a UBC (used beverage can) ingot into which a used aluminum beverage can in a molten state is formed is also usable.

The Cu content in the aluminum plate is preferably 0.00 wt % or more, more preferably at least 0.01 wt % and even more preferably at least 0.02 wt % but is preferably 0.15 wt % or less, more preferably 0.11 wt % or less and even more preferably 0.03 wt % or less. An aluminum plate containing 0.07 to 0.09 wt % of Si, 0.20 to 0.29 wt % of Fe, not more than 0.03 wt % of Cu, not more than 0.01 wt % of Mn, not more than 0.01 wt % of Mg, not more than 0.01 wt % of Cr, not more than 0.01 wt % of Zn, not more than 0.02 wt % of Ti and not less than 99.5 wt % of Al is particularly preferred.

The present applicant has disclosed related art concerning JIS 1050 materials in JP 59-153861 A, JP 61-51395 A, JP 62-146694 A, JP 60-215725 A, JP 60-215726 A, JP 60-215727 A, JP 60-216728 A, JP 61-272367 A, JP 58-11759 A, JP 58-42493 A, JP 58-221254 A, JP 62-148295 A, JP 4-254545 A, JP 4-165041 A, JP 3-68939 B (the term “JP XXXX-XXXXXX B” as used herein means an “examined Japanese patent publication”), JP 3-234594 A, JP 1-47545 B and JP 62-140894 A. The art described in JP 1-35910 B and JP 55-28874 B is also known.

This applicant has also disclosed related art concerning JIS 1070 materials in JP 7-81264 A, JP 7-305133 A, JP 8-49034 A, JP 8-73974 A, JP 8-108659 A and JP 8-92679 A.

In addition, this applicant has disclosed related art concerning aluminum-magnesium alloys in JP 62-5080 B, JP 63-60823 B, JP 3-61753 B, JP 60-203496 A, JP 60-203497 A, JP 3-11635 B, JP 61-274993 A, JP 62-23794 A, JP 63-47347 A, JP 63-47348 A, JP 63-47349 A, JP 64-1293 A, JP 63-135294 A, JP 63-87288 A, JP 4-73392 B, JP 7-100844 B, JP 62-149856 A, JP 4-73394 B, JP 62-181191 A, JP 5-76530 B, JP 63-30294 A and JP 6-37116 B. The related art is disclosed also in JP 2-215599 A, JP 61-201747 A, and so forth.

This applicant has disclosed related art concerning aluminum-manganese alloys in JP 60-230951 A, JP 1-306288 A and JP 2-293189 A. The related art is disclosed also in JP 54-42284 B, JP 4-19290 B, JP 4-19291 B, JP 4-19292 B, JP 61-35995 A, JP 64-51992 A, JP 4-226394 A, U.S. Pat. No. 5,009,722, U.S. Pat. No. 5,028,276, and so forth.

The present applicant has disclosed related art concerning aluminum-manganese-magnesium alloys in JP 62-86143 A and JP 3-222796 A. The related art is disclosed also in JP 63-60824 B, JP 60-63346 A, JP 60-63347 A, JP 1-293350 A, EP 223,737, U.S. Pat. No. 4,818,300, GB 1,222,777, and so forth.

Also, this applicant has disclosed related art concerning aluminum-zirconium alloys in JP 63-15978 B and JP 61-51395 A. The related art is disclosed also in JP 63-143234 A, JP 63-143235 A, and so forth.

Aluminum-magnesium-silicon alloys are described in GB 1,421,710, and so forth.

The aluminum alloy may be rendered into sheet stock by the following method, for example. An aluminum alloy melt that has been adjusted to a given alloying ingredient content is initially subjected to cleaning treatment by an ordinary method, and then is cast. Cleaning treatment, which is carried out to remove hydrogen and other unnecessary gases from the melt, typically involves flux treatment; degassing treatment using argon gas, chlorine gas or the like; filtering treatment using, for example, what is referred to as a rigid media filter (e.g., ceramic tube filters, ceramic foam filters), a filter that employs a filter medium such as alumina flakes or alumina balls, or a glass cloth filter; or a combination of degassing treatment and filtering treatment.

Cleaning treatment is preferably carried out to prevent defects due to foreign matter such as nonmetallic inclusions and oxides in the melt, and defects due to dissolved gases in the melt. The filtration of melts is described in, for example, JP 6-57432 A, JP 3-162530 A, JP 5-140659 A, JP 4-231425 A, JP 4-276031 A, JP 5-311261 A, and JP 6-136466 A. The degassing of melts is described in, for example, JP 5-51659 A and JP 5-49148 U. The present applicant discloses related art concerning the degassing of melts in JP 7-40017 A.

Next, the melt that has been subjected to cleaning treatment as described above is cast. Casting processes include those which use a stationary mold, such as direct chill casting, and those which use a moving mold, such as continuous casting.

In direct chill casting, the melt is solidified at a cooling speed of 0.5 to 30° C. per second. At less than 0.5° C./sec, many coarse intermetallic compounds may be formed. When direct chill casting is carried out, an ingot having a thickness of 300 to 800 mm can be obtained. If necessary, this ingot is scalped by a conventional method, generally removing 1 to 30 mm, and preferably 1 to 10 mm, of material from the surface. The ingot may also be optionally soaked, either before or after scalping. In the case where soaking is carried out, the ingot is heat treated at 450 to 620° C. for 1 to 48 hours to prevent the coarsening of intermetallic compounds. The effects of soaking treatment may be inadequate if heat treatment is shorter than one hour. If soaking treatment is not carried out, this can have the advantage of lowering costs.

The ingot is then hot-rolled and cold-rolled, giving a rolled aluminum plate. A temperature of 350 to 500° C. at the start of hot rolling is appropriate. Intermediate annealing may be carried out before or after hot rolling, or even during hot rolling. The intermediate annealing conditions consist of 2 to 20 hours of heating at 280 to 600° C., and preferably 2 to 10 hours of heating at 350 to 500° C., in a batch-type annealing furnace, or of heating for up to 6 minutes at 400 to 600° C., and preferably up to 2 minutes at 450 to 550° C., in a continuous annealing furnace. Using a continuous annealing furnace to heat the rolled plate at a temperature rise rate of 10 to 200° C./sec enables a finer crystal structure to be achieved.

The aluminum plate that has been finished by the above process to a given thickness of, say, 0.1 to 0.5 mm may then be flattened with a leveling machine such as a roller leveler or a tension leveler. Flattening may be carried out after the aluminum plate has been cut into discrete sheets. However, to enhance productivity, it is preferable to carry out such flattening with the rolled aluminum plate in the state of a continuous roll. The plate may also be passed through a slitter line to cut it to a predetermined width. A thin film of oil may be provided on the aluminum plate to prevent scuffing due to rubbing between adjoining aluminum plates. Suitable use may be made of either a volatile or non-volatile oil film, as needed.

Continuous casting processes that are industrially carried out include processes which use cooling rolls, such as the twin roll process (Hunter process) and the 3C process, the twin belt process (Hazelett process), and processes which use a cooling belt or a cooling block, such as the Alusuisse Caster II process. When a continuous casting process is used, the melt is solidified at a cooling rate of 100 to 1,000° C./sec. Continuous casting processes generally have a faster cooling rate than direct chill casting processes, and so are characterized by the ability to achieve a higher solid solubility of alloying ingredients in the aluminum matrix. Technology relating to continuous casting processes that has been disclosed by the present applicant is described in, for example, JP 3-79798 A, JP 5-201166 A, JP 5-156414 A, JP 6-262203 A, JP 6-122949 A, JP 6-210406 A and JP 6-26308 A.

When continuous casting is carried out, such as by a process involving the use of cooling rolls (e.g., the Hunter process), the melt can be directly and continuously cast as a plate having a thickness of 1 to 10 mm, thus making it possible to omit the hot rolling step. Moreover, when use is made of a process that employs cooling belts (e.g., the Hazelett process), a plate having a thickness of 10 to 50 mm can be cast. Generally, by positioning a hot-rolling roll immediately downstream of the caster, the cast plate can then be successively rolled, enabling a continuously cast and rolled plate with a thickness of 1 to 10 mm to be obtained.

These continuously cast and rolled plates are then subjected to such processes as cold rolling, intermediate annealing, flattening and slitting in the same way as described above for direct chill casting, and thereby finished to a plate thickness of 0.1 to 0.5 mm, for instance. Technology disclosed by the present applicant concerning the intermediate annealing conditions and cold rolling conditions in a continuous casting process is described in, for example, JP 6-220593 A, JP 6-210308 A, JP 7-54111 A and JP 8-92709 A.

The aluminum plate used in the present invention is well-tempered in accordance with H18 defined in JIS.

It is desirable for the aluminum plate manufactured as described above to have the following properties.

For the aluminum plate to achieve the stiffness required of a lithographic printing plate support, it should have a 0.2% proof strength of preferably at least 120 MPa. To ensure some degree of stiffness even when burning treatment has been carried out, the 0.2% proof strength following 3 to 10 minutes of heat treatment at 270° C. should be preferably at least 80 MPa, and more preferably at least 100 MPa. In the case where the aluminum plate is required to have a high stiffness, use may be made of an aluminum material containing magnesium or manganese. However, because a higher stiffness lowers the ease with which the plate can be fit onto the plate cylinder of the printing press, the plate material and the amounts of minor components added thereto are suitably selected according to the intended application. Related technology disclosed by the present applicant is described in, for example, JP 7-126820 A and JP 62-140894 A.

The aluminum plate more preferably has a tensile strength of 160±15 N/mm², a 0.2% proof strength of 140±15 MPa, and an elongation as defined in JIS Z2241 and Z2201 of 1 to 10%.

Because the crystal structure at the surface of the aluminum plate may give rise to a poor surface quality when chemical graining treatment or electrochemical graining treatment is carried out, it is preferable that the crystal structure not be too coarse. The crystal structure at the surface of the aluminum plate has a width of preferably up to 200 μm, more preferably up to 100 μm, and most preferably up to 50 μm. Moreover, the crystal structure has a length of preferably up to 5,000 μm, more preferably up to 1,000 μm, and most preferably up to 500 μm. Related technology disclosed by the present applicant is described in, for example, JP 6-218495 A, JP 7-39906 A and JP 7-124609 A.

It is preferable for the alloying ingredient distribution at the surface of the aluminum plate to be reasonably uniform because non-uniform distribution of alloying ingredients at the surface of the aluminum plate sometimes leads to a poor surface quality when chemical graining treatment or electrochemical graining treatment is carried out. Related technology disclosed by the present applicant is described in, for example, JP 6-48058 A, JP 5-301478 A and JP 7-132689 A.

The size or density of intermetallic compounds in an aluminum plate may affect chemical graining treatment or electrochemical graining treatment. Related technology disclosed by the present applicant is described in, for example, JP 7-138687 A and JP 4-254545 A.

The aluminum plate used in this invention is in the form of a continuous sheet or discrete sheets. That is, it may be either an aluminum web or a cut sheet of aluminum having a size which corresponds to the presensitized plates that will be shipped as the final products.

Because scratches and other marks on the surface of the aluminum plate may become defects when the plate is fabricated into a lithographic printing plate support, it is essential to minimize the formation of such marks prior to the surface treatment operations for rendering the aluminum plate into a lithographic printing plate support. It is thus desirable for the aluminum plate to be stably packed in such a way that it will not be easily damaged during transport.

When the aluminum plate is in the form of a web, it may be packed by, for example, laying hardboard and felt on an iron pallet, placing corrugated cardboard doughnuts on either side of the product, wrapping everything with polytubing, inserting a wooden doughnut into the opening at the center of the coil, stuffing felt around the periphery of the coil, tightening steel strapping about the entire package, and labeling the exterior. In addition, polyethylene film can be used as the outer wrapping material, and needled felt and hardboard can be used as the cushioning material. Various other forms of packing exist, any of which may be used so long as the aluminum plate can be stably transported without being scratched or otherwise marked.

The aluminum plate used in the present invention has a thickness of about 0.1 to 0.6 mm, preferably 0.15 to 0.4 mm, and more preferably 0.2 to 0.3 mm. This thickness can be changed as appropriate based on such considerations as the size of the printing press, the size of the printing plate and the desires of the user.

<Surface Treatment>

In the method of manufacturing a lithographic printing plate support of the present invention, the aluminum plate as described above is subjected to at least a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, and an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm (first hydrochloric acid electrolysis), with the treatments being performed in this order, so as to obtain a lithographic printing plate support.

The method of manufacturing a lithographic printing plate support of the present invention may include various other processes than the above. In a preferred illustrative case, the aluminum plate as described above is subjected to at least a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, an etching treatment in an aqueous alkali solution (first alkali etching treatment), an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm (first hydrochloric acid electrolysis), an etching treatment in an aqueous alkali solution (second alkali etching treatment), an electrochemical graining treatment in an aqueous solution containing hydrochloric acid (second hydrochloric acid electrolysis), an etching treatment in an aqueous alkali solution (third alkali etching treatment), and an anodizing treatment, with the treatments being performed in this order.

Also preferred are a method including a desmutting treatment in an aqueous acid solution to be performed subsequent to at least one of the etching treatments in an aqueous alkali solution, and that further including a hydrophilizing treatment to be performed subsequent to the anodizing treatment.

The exemplary processes as above are described in detail below.

<Mechanical Graining Treatment>

In the present invention, the aluminum plate as described above is subjected to a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) of the plate is 0.25 μm or more but less than 0.40 μm, preferably 0.28 to 0.37 μm, and more preferably 0.30 to 0.35 μm.

The average surface roughness R_(a) within such a range attained by the mechanical graining treatment not only allows the reduction in the energy required for the first hydrochloric acid electrolysis but also provides a presensitized plate of high sensitivity by preventing a local formation of deep recesses as described before.

The mechanical graining treatment is performed by a brush grinding method (brush graining method) in which the surface of an aluminum plate is ground by using one kind of brush (or brushes), or two or more kinds of brushes with different bristle diameters, while feeding a slurry containing an abrasive to the plate surface. Preferred examples of the method include a wire brush graining method using metal wires to scratch the aluminum surface, and a brush graining method for the surface graining with nylon brushes.

In a general brush graining method, the surface of the aluminum plate as described above is rubbed on one or both sides of the plate with rotating roller brushes (brush rolls) onto which a slurry containing an abrasive is being sprayed. A roller brush used in the method has a cylindrical body constituting a roller-shaped base in which brush bristles (bristle members), including bristles made of a synthetic resin such as nylon (registered trademark), polypropylene and polyvinyl chloride, animal bristles, and steel wires, of a uniform length are set with a uniform distribution. Alternatively, the roller brush may have whisks of bristles set in the small holes provided in the base, or may be of a channel roller type.

The brush bristles preferably have a flexural modulus of 10,000 to 40,000 kgf/cm², more preferably 15,000 to 35,000 kgf/cm², and their stiffness is preferably up to 500 gf, more preferably up to 400 gf.

A material which fully meets such property requirements and is suitably used for the brush bristles is nylon, to be more specific, nylon 6, nylon 6.6, nylon 6.10, and so forth. Nylon 6.10 is particularly preferable in view of its tensile strength, abrasion resistance, size stability during water absorption, flexural-strength, heat resistance, recovery, and so forth.

The brush bristles made of nylon preferably have a low water absorbing rate. In this regard, preferred examples include Nylon Bristle 200T (made of nylon 6.10; softening point, 180° C.; melting point, 212 to 214° C.; specific gravity, 1.08 to 1.09; moisture regain, 1.4 to 1.8 at a temperature of 20° C. and a relative humidity of 65%, 2.2 to 2.8 at 20° C. and a relative humidity of 100%,; dry tensile strength, 4.5 to 6 g/d; dry tensile elongation, 20 to 35%; boiled water shrinkage factor, 1 to 4%; dry resistance to stretching, 39 to 45 g/d; Young's modulus (dry), 380 to 440 kg/mm²) manufactured by Toray Corporation.

The length of the bristles on a roller base is preferably 10 to 200 mm. The density of the bristles set in a roller base is preferably 30 to 1,000 bristles, more preferably 50 to 300 bristles, per 1 cm².

The bristle diameter is preferably 0.24 to 0.83 mm. A diameter within such a range readily ensures a desirable average surface roughness (R_(a) which is 0.25 μm or more but less than 0.40 μm), resulting in an improvement of the scumming resistance of a blanket.

The brush bristles are preferably circular in cross section.

The number of brushes is preferably 1 to 10, and more preferably 1 to 6. Two or more kinds of brushes (e.g., roller brushes) with different bristle diameters may be used in combination as described in JP 6-135175 A. In that case, it is also possible to use a plurality of brushes (two or three brushes, for instance) for each kind. When two or more kinds of brushes are used, it is conventional that the brush (brushes) to be initially used for brush graining is to be called the first brush (brushes) while that (those) to be used lastly be called the second brush (brushes).

When a roller brush is used, it is preferable to appropriately choose the revolution number of the brush within the range of 100 to 500 rpm.

Preferably, a roller brush is rotated in the same direction as the direction of advance of the aluminum plate as shown in FIG. 1. If many roll brushes are used, part of them may be rotated in the reverse direction. The amount of a roller brush press is preferably controlled with the load on the driving motor which rotates the brush, to be more specific, controlled by setting the power consumption of the motor at 1.0 to 15 kW. Support rollers used in the method are those having a rubber or metal face and being well kept straight in shape.

The abrasive-containing slurry is preferably prepared by dispersing a known abrasive such as pumice stone, silica sand, aluminum hydroxide, alumina powder, silicon carbide, silicon nitride, volcanic ash, volcanic foam, carborundum and emery as described in JP 6-135175 A and JP 50-40047 B which has an average particle diameter of 1 to 50 μm (preferably 20 to 45 μm) in water so as to obtain a slurry with a specific gravity of 1.05 to 1.3. The average particle diameter as used herein refers to a particle diameter corresponding to the cumulative volume of 50% when a cumulative frequency distribution curve showing the relation between the cumulative volume of the abrasive particles in a slurry and their particle diameter is prepared. An average particle diameter of the abrasive within such a range as above allows a high graining efficiency and a suitably small graining pitch.

The abrasive-containing slurry may additionally contain thickening agent, dispersant (surfactant, for instance), preservative, and so forth.

The abrasive-containing slurry is suitably fed to the surface of an aluminum plate by spraying, for instance. The method as described in JP 55-74898 A, JP 61-162351 A or JP 63-104889 A may be used for the feed of the slurry. It is also possible to brush-grinding the aluminum plate surface in an aqueous slurry containing a mixture of alumina and quartz with a weight ratio of 95:5 to 5:95 as described in JP 9-509108 A. The average particle diameter of the above mixture is preferably within the range of 1 to 40 μm, especially 1 to 20 μm.

According to the present invention, an average surface roughness R_(a) of 0.25 μm or more but less than 0.40 μm can be imparted to the aluminum plate subjected to the mechanical graining treatment by appropriately modifying such conditions as the revolution number of brushes, the number of brushes, the direction in which brushes are rotated, the bristle diameter of brushes, the bristle length of brushes, the diameter of roller brushes, the kind of abrasive, the particle size of abrasive, the specific gravity of abrasive-containing slurry, the flow rate of abrasive-containing slurry, the pressing force (indentation amount) of brushes, and the advancing speed of aluminum plate.

Particularly preferable ranges of such conditions are as follows.

The revolution number of brushes is 150 to 250 rpm;

-   -   the number of brushes is 1 to 3;     -   the brush-rotating direction is the same as the aluminum         plate-advancing direction;     -   the bristle diameter of brushes is 0.24 to 0.3 mm;     -   the bristle length of brushes is 30 to 100 mm;     -   the roller-brush diameter is 300 to 600 mm;     -   the abrasive to be used is aluminum hydroxide, or classified         silica sand, or ground and classified volcanic foam;     -   the particle size of abrasive is 20 to 40 μm as the average         particle diameter;     -   the specific gravity of abrasive-containing slurry is 1.05 to         1.18; and     -   the aluminum plate-advancing speed is 30 to 300 m/min.

The apparatus suitable for performing the mechanical graining treatment by the brush graining method as described above can be exemplified by the apparatus as disclosed in JP 6-135175 A or JP 50-40047 B.

FIG. 1 is a side view conceptually showing processes of brush graining in the method of manufacturing a lithographic printing plate support according to the present invention.

As seen from FIG. 1, roller brushes 2 and 4 are located on one side of an aluminum plate 1 and support rollers 5 and 6 as well as 7 and 8, each two supporting the brush 2 or 4, are located on the other side of the aluminum plate 1. Each two support rollers 5 and 6 or 7 and 8 are so arranged that the shortest distance between their outer surfaces may be less than the outer diameter of the roller brush 2 or 4 supported by them. The aluminum plate 1 is pressed by the roller brushes 2 and 4 a bit down into the spaces between the support rollers 5 and 6 as well as 7 and 8, respectively, and, as such, caused to advance at a constant speed. The surface of the advancing aluminum plate 1 is brush grained by feeding an abrasive-containing slurry 3 onto the plate and rotating the roller brushes.

In the present invention, the average surface roughness R_(a) of the aluminum plate is measured as follows: Two-dimensional roughness measurement is conducted using a stylus-type roughness tester (e.g., Surfcom 575 manufactured by Tokyo Seimitsu Co., Ltd.). The average roughness R_(a) as defined in ISO 4287 is measured five times, and the mean of the five measurements is used as the value of the average surface roughness.

The conditions of the two-dimensional roughness measurement are described below.

<Measurement Conditions>

Cutoff value, 0.8 mm; slope correction, FLAT-ML; measurement length, 3 mm; vertical magnification, 10,000×; scan rate, 0.3 mm/sec; stylus tip diameter, 2 μm.

The longitudinal to transversal length ratio of the recesses (major-axial to minor-axial length ratio of the elliptical pits) formed on the surface of the aluminum plate as above is measured as follows, for instance: The surface of the aluminum plate is photographed at a magnification of 500 to 1,000, preferably 700 to 800, from right above with an electron microscope. In an electron micrograph obtained, at least 50 elliptical recesses are extracted, the major-axial and minor-axial lengths are read for each recess to find the major-axial to minor-axial length ratio, and the average is calculated.

The number of the recesses formed can be determined also by photographing the surface of the aluminum plate from right above with an electron microscope.

<First Alkali Etching Treatment>

In the present invention, the aluminum plate subjected to the mechanical graining treatment using a brush and a slurry containing an abrasive is then preferably subjected to a first alkali etching treatment for etching the plate surface in an aqueous alkali solution.

In the first alkali etching treatment, the surface layer of the aluminum plate as described before is dissolved by bringing the aluminum plate into contact with an alkali solution. The purpose of this treatment is to dissolve the edges of the asperities provided on the aluminum plate surface by the mechanical graining treatment and a natural oxide film as well and remove the abrasive, aluminum scraps, and so forth digging into the aluminum plate surface so as to enable an effective formation of uniform recesses in the first hydrochloric acid electrolysis to be performed later.

In the first alkali etching treatment, the etching amount, namely amount of material removed by etching, is preferably at least 1 g/m², more preferably at least 1.5 g/m², and further preferably at least 2 g/m², but preferably not more than 10 g/m², more preferably not more than 8 g/m², and further preferably not more than 6 g/m². If the lower limit of the etching amount lies in such a range as above, uniform pits can be formed in the first hydrochloric acid electrolysis and, moreover, treatment irregularities can be prevented. On the other hand, an upper limit of the etching amount in the above range allows a decrease in the aqueous solution required, which is economically advantageous.

Alkalis that may be used in the alkali solution are exemplified by caustic alkalis and alkali metal salts. Specific examples of suitable caustic alkalis include sodium hydroxide and potassium hydroxide. Specific examples of suitable alkali metal salts include alkali metal silicates such as sodium metasilicate, sodium silicate, potassium metasilicate and potassium silicate; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal aluminates such as sodium aluminate and potassium aluminate; alkali metal aldonates such as sodium gluconate and potassium gluconate; and alkali metal hydrogenphosphates such as sodium secondary phosphate, potassium secondary phosphate, sodium primary phosphate and potassium primary phosphate. Among others, caustic alkali solutions and solutions containing both a caustic alkali and an alkali metal aluminate are preferred on account of the high etch rate and low cost. An aqueous solution of sodium hydroxide is especially preferred.

In the first alkali etching treatment, the alkali solution preferably has a concentration of at least 10 g/L, and more preferably at least 30 g/L, but preferably not more than 500 g/L, and more preferably not more than 450 g/L.

It is desirable for the alkali solution to contain aluminum ions. The aluminum ion concentration is preferably at least 1 g/L, and more preferably at least 3 g/L, but preferably not more than 200 g/L, and more preferably not more than 150 g/L. Such an alkali solution can be prepared from, for example, water, a 48 wt % solution of sodium hydroxide in water, and sodium aluminate.

In the first alkali etching treatment, the alkali solution temperature is preferably at least 30° C., and more preferably at least 50° C., but preferably not more than 80° C., and more preferably not more than 75° C.

The treatment time in the first alkali etching treatment is preferably at least 1 second, and more preferably at least 2 seconds, but preferably not more than 30 seconds, and more preferably not more than 15 seconds.

When the aluminum plate is continuously etched, the aluminum ion concentration in the alkali solution rises and the etching amount at which the aluminum plate is treated changes. It is thus preferable to control the etching solution composition as follows.

First, a matrix of the electrical conductivity, specific gravity and temperature or a matrix of the conductivity, ultrasonic wave propagation velocity and temperature is prepared with respect to a matrix of the sodium hydroxide concentration and the aluminum ion concentration. The solution composition is then determined based on either the conductivity, specific gravity and temperature or the conductivity, ultrasonic wave propagation velocity and temperature, and sodium hydroxide and water are added up to control target values for the solution composition. Next, the etching solution which has increased in volume with the addition of sodium hydroxide and water is allowed to overflow from a circulation tank, thereby keeping the amount of solution constant. The sodium hydroxide added may be industrial grade 40 to 60 wt % sodium hydroxide.

The conductivity meter and hydrometer used to measure electrical conductivity and specific gravity, respectively, are each preferably temperature-compensated instruments. The hydrometer is preferably a pressure differential hydrometer.

Illustrative examples of methods for bringing the aluminum plate into contact with the alkali solution include a method in which the aluminum plate is passed through a tank filled with an alkali solution, a method in which the aluminum plate is immersed in an alkali solution contained in a tank, and a method in which the surface of the aluminum plate is sprayed with an alkali solution.

The most desirable of these is a method that involves spraying the surface of the aluminum plate with an alkali solution. Specifically, in such a method, the etching solution is sprayed onto the aluminum plate from a spray line, which bears 2 to 5 mm diameter openings at a pitch of 10 to 50 mm, at a rate of 10 to 100 L/min per spray line. It is preferred that two or more spray lines are employed.

Following the completion of alkali etching treatment, it is desirable to remove the etching solution from the aluminum plate with nip rollers, subject the plate to rinsing treatment with water for 1 to 10 seconds, then remove the water with nip rollers.

Rinsing treatment is preferably carried out by rinsing with a rinsing apparatus that uses a free-falling curtain of water and then rinsing further with a spray line.

FIG. 2 is a schematic cross-sectional view of an apparatus 100 for carrying out rinsing treatment with a free-falling curtain of water. As shown in FIG. 2, the apparatus 100 that carries out rinsing with a free-falling curtain of water has a water holding tank 104 that holds water 102, a pipe 106 that feeds water to the water holding tank 104, and a flow distributor 108 that supplies a free-falling curtain of water from the water holding tank 104 to an aluminum plate 101.

In this apparatus 100, the pipe 106 feeds water 102 to the water holding tank 104. When the water 102 overflows the water holding tank 104, it is distributed by the flow distributor 108 and the free-falling curtain of water is supplied to the aluminum plate 101. A flow rate of 10 to 100 L/min is preferred when this apparatus 100 is used. The distance L between the apparatus 100 and the aluminum plate 101 over which the water 102 exists as a free-falling liquid curtain is preferably from 20 to 50 mm. Moreover, it is preferable for the aluminum plate to be inclined at an angle α to the horizontal of 30 to 80°.

By using an apparatus like that in FIG. 2 which rinses the aluminum plate with a free-falling curtain of water, the aluminum plate can be uniformly rinsed. This in turn makes it possible to enhance the uniformity of treatment carried out prior to rinsing.

A preferred example of an apparatus that carries out rinsing treatment with a free-falling curtain of water is described in JP 2003-96584 A.

Rinsing with a spray line may be carried out by the use of, for instance, a spray line having a plurality of spray tips disposed along the width of the aluminum plate, each of which discharges a fanned-out spray of water. The interval between spray tips is preferably 20 to 100 mm, and the amount of water discharged per spray tip is preferably 0.5 to 20 L/min. The use of a plurality of spray lines is preferred.

<First Desmutting Treatment>

After the first alkali etching treatment, it is preferable to perform acid pickling (first desmutting treatment) to remove contaminants (smut) remaining on the surface of the aluminum plate. Desmutting is carried out by bringing the aluminum plate into contact with an acidic solution.

Examples of acids that may be used include nitric acid, sulfuric acid, phosphoric acid, chromic acid, hydrofluoric acid, and tetrafluoroboric acid.

The composition of the desmutting treatment solution may be controlled based on the electrical conductivity and temperature, or on the electrical conductivity, specific gravity and temperature, or on the electrical conductivity, ultrasonic wave propagation velocity and temperature, which parameters are corresponding to a matrix of the acidic solution concentration and the aluminum ion concentration.

In the first desmutting treatment, it is preferable to use an acidic solution containing 1 to 400 g/L of an acid and 0.1 to 5 g/L of aluminum ions.

The temperature of the acidic solution is preferably at least 20° C., and more preferably at least 30° C., but preferably not more than 70° C., and more preferably not more than 60° C.

In the first desmutting treatment, the treatment time is preferably at least 1 second, and more preferably at least 4 seconds, but preferably not more than 60 seconds, and more preferably not more than 40 seconds.

Illustrative examples of the method of bringing the aluminum plate into contact with the acidic solution include passing the aluminum plate through a tank filled with the acidic solution, immersing the aluminum plate in the acidic solution contained in a tank, and spraying the acidic solution onto the surface of the aluminum plate.

Of these, a method in which the acidic solution is sprayed onto the surface of the aluminum plate is preferred. Specifically, in such a method, the desmutting treatment solution is sprayed onto the aluminum plate from a spray line bearing 2 to 5 mm diameter openings at a pitch of 10 to 50 mm at a rate of 10 to 100 L/min per spray line. It is preferable that two or more spray lines are employed.

After desmutting treatment, it is preferable to remove the solution with nip rollers, then carry out rinsing treatment with water for 1 to 10 seconds and again remove the water with nip rollers.

Rinsing treatment is the same as the rinsing treatment following alkali etching treatment. The amount of water discharged per spray tip, however, is preferably from 1 to 20 L/min.

<First Hydrochloric Acid Electrolysis>

In the present invention, the aluminum plate after the mechanical graining treatment, or that after the first alkali etching treatment or first desmutting treatment subsequent to the mechanical graining treatment, is subjected to a first hydrochloric acid electrolysis in which electrochemical graining is carried out in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm, preferably 0.43 to 0.52 μm.

If the average surface roughness R_(a) is within such a range as above owing to the first hydrochloric acid electrolysis, the aluminum plate surface will have a uniform asperities (pits) of a regular shape provided thereon. In consequence, a presensitized plate which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate can be obtained.

The aqueous solution containing hydrochloric acid that is to be used in the present invention may be any such solution as used in conventional electrochemical graining treatments employing direct or alternating current. Specifically, it may be an aqueous solution containing 1 to 30 g/L, preferably 2 to 10 g/L of hydrochloric acid, to which one or more nitrate compounds containing nitrate ion such as aluminum nitrate, sodium nitrate and ammonium nitrate; chloride compounds containing chloride ion such as aluminum chloride, sodium chloride and ammonium chloride; or sulfate compounds containing sulfate ion such as aluminum sulfate, sodium sulfate and ammonium sulfate may be added at a level of 1 g/L to saturation. Preferred is an aqueous solution of hydrochloric acid containing 0.1 to 10 g/L, more preferably 1 to 5 g/L of sulfate ions. A compound which forms a complex with copper may also be added in an amount of 1 to 200 g/L.

A metal present in an aluminum alloy, such as iron, copper, manganese, nickel, titanium, magnesium and silicon, may be dissolved in the aqueous solution containing hydrochloric acid. Hypochlorous acid or hydrogen peroxide may be added to the solution in an amount of 1 to 100 g/L.

Particularly preferred is an aqueous solution of hydrochloric acid with a desirable hydrochloric acid concentration of 5 to 20 g/L, whose aluminum ion concentration is adjusted to 4 to 20 g/L, preferably 4.3 to 15 g/L, by adding 27 to 63 g/L of an aluminum salt (aluminum chloride: AlCl₃.6H₂O). If electrochemical graining treatment is performed using such an aqueous solution of hydrochloric acid, the surface profile of the treated aluminum plate will be uniform and no irregularities will be generated in the treatment irrespective of the purity of the rolled aluminum plate used. Accordingly, a presensitized plate which has both an excellent scumming resistance and a good press life when made into a lithographic printing plate can be obtained.

Substances added to the aqueous solution containing hydrochloric acid, electrolyzers, power supplies, current densities, flow rates and temperatures which are to be employed in this treatment may be those employed for a known electrochemical graining. The power supply for electrochemical graining may be of a direct or alternating current type, with an alternating current power supply being particularly preferred.

In the first hydrochloric acid electrolysis, the total amount of electricity used for the anodic reaction is preferably 100 to 500 C/dm², more preferably 200 to 400 C/dm², and further preferably 300 to 350 C/dm². If the total amount of electricity is within such a range as above, it is readily possible to impart an average surface roughness R_(a) of 0.40 to 0.55 μm to the aluminum plate surface after the first hydrochloric acid electrolysis. In that case, pits with an average aperture diameter of 1 to 15 μm are formed on the surface of the aluminum plate which provide a crater-like large undulation on the plate surface while having fine recesses with an average aperture diameter of 0.01 to 0.4 μm provided on their own surfaces.

In the case where electrolytic graining treatment is performed in an electrolytic cell comprising a main electrolytic cell and an auxiliary anode cell as will be described later, it is preferable that the amount of electricity used is 10 to 250 C/dm² for each cell and the amount of electricity used for the treatment in the individual cells is 100 to 500 C/dm² in total. The flow rate, current density, amount of electricity, and other conditions may be the same or different between the cells. Such conditions can be chosen suitably for a desired profile of grained surface.

The first hydrochloric acid electrolysis may follow the electrochemical graining method (electrolytic graining method) as described in JP 48-28123 B and GB 896,563, for example. While this electrolytic graining method uses an alternating current with a sinusoidal waveform, a special waveform such as described in JP 52-58602 A will also do. In addition, a waveform as described in JP 3-79799 A may be used. Moreover, the methods as described in JP 55-158298 A, JP 56-28898 A, JP 52-58602 A, JP 52-152302 A, JP 54-85802 A, JP 60-190392 A, JP 58-120531 A, JP 63-176187 A, JP 1-5889 A, JP 1-280590 A, JP 1-118489 A, JP 1-148592 A, JP 1-178496 A, JP 1-188315 A, JP 1-154797 A, JP 2-235794 A, JP 3-260100 A, JP 3-253600 A, JP 4-72079 A, JP 4-72098 A, JP 3-267400 A and JP 1-141094 A are also applicable. Besides the aforementioned, it is also possible to perform electrolysis using an alternating current with a special frequency which has been proposed as a method for producing an electrolytic capacitor. It is described for example in U.S. Pat. No. 4,276,129 and U.S. Pat. No. 4,676,879.

Various electrolytic cells and power supplies have been proposed for use in electrolytic treatment. For example, use may be made of those described in U.S. Pat. No. 4,203,637, JP 56-123400 A, JP 57-59770 A, JP 53-12738 A, JP 53-32821 A, JP 53-32822 A, JP 53-32823 A, JP 55-122896 A, JP 55-132884 A, JP 62-127500 A, JP 1-52100 A, JP 1-52098 A, JP 60-67700 A, JP 1-230800 A, JP 3-257199 A, JP 52-58602 A, JP 52-152302 A, JP 53-12738 A, JP 53-12739 A, JP 53-32821 A, JP 53-32822 A, JP 53-32833 A, JP 53-32824 A, JP 53-32825 A, JP 54-85802 A, JP 55-122896 A, JP 55-132884 A, JP 48-28123 B, JP 51-7081 B, JP 52-133838 A, JP 52-133840 A, JP 52-133844 A, JP 52-133845 A, JP 53-149135 A and JP 54-146234 A.

When the aluminum plate is continuously subjected to electrolytic graining treatment, the aluminum ion concentration in the aqueous solution of hydrochloric acid rises and the shape of the asperities provided on the aluminum plate by the hydrochloric acid electrolysis changes. It is thus preferable to control the composition of the hydrochloric acid electrolyte solution as follows.

First, a matrix of the electrical conductivity, specific gravity and temperature or a matrix of the conductivity, ultrasonic wave propagation velocity and temperature is prepared with respect to a matrix of the hydrochloric acid concentration and the aluminum ion concentration. The solution composition is then determined based on either the conductivity, specific gravity and temperature or the conductivity, ultrasonic wave propagation velocity and temperature, and hydrochloric acid and water are added up to control target values for the solution composition. Next, the electrolyte solution which has increased in volume with the addition of hydrochloric acid and water is allowed to overflow from a circulation tank, thereby keeping the amount of solution constant. The hydrochloric acid added may be industrial grade 30 to 70 wt % hydrochloric acid.

The conductivity meter and hydrometer used to measure electrical conductivity and specific gravity, respectively, are each preferably temperature-compensated instruments. The hydrometer is preferably a pressure differential hydrometer.

In view of an improved measurement accuracy, the electrolyte solution samples to be used for the measurement of solution composition are preferably regulated in temperature to a certain value (40±0.5° C., for instance) with a heat exchanger other than that for the electrolyte solution before they are used for the measurement.

By adding and using a compound capable of forming a complex with copper, uniform graining may be carried out even on an aluminum plate having a high copper content. Examples of the compound capable of forming a complex with copper include ammonia; amines obtained by substituting the hydrogen atom on ammonia with a hydrocarbon group (of an aliphatic, aromatic, or other nature), such as methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, cyclohexylamine, triethanolamine, triisopropanolamine and ethylenediamine tetraacetate (EDTA); and metal carbonates such as sodium carbonate, potassium carbonate and potassium hydrogencarbonate. Additional compounds suitable for this purpose include ammonium salts such as ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium phosphate and ammonium carbonate.

The temperature of the aqueous solution containing hydrochloric acid is preferably 20 to 45° C., and more preferably 30 to 35° C.

No particular limitation is imposed on the AC power supply waves used in the electrochemical graining treatment. For example, sinusoidal (sine), square, trapezoidal or triangular waves may be used. Preferred are sinusoidal, square or trapezoidal waves and sinusoidal or trapezoidal ones are especially preferred. “Trapezoidal” waves are waves having such a waveform as shown in FIG. 3. In this trapezoidal waveform, the time (TP) in which the current value changes from zero to a peak is preferably 0.5 to 3 msec. If the TP is more than 3 msec, a uniform graining is hard to accomplish and, as a result, the scumming resistance of a lithographic printing plate prepared is liable to be reduced.

A trapezoidal wave alternating current with a duty ratio (ta/T) of 0.33 to 0.66 is usable, and the duty ratio (ta/T) is preferably 0.5 in an indirect power supplying system dispensing with a conductor roll for aluminum as described in JP 5-195300 A.

While a trapezoidal wave alternating current with a frequency of 0.1 to 120 Hz is usable, the frequency is preferably 50 to 70 Hz in terms of equipment. If it is lower than 50 Hz, the carbon electrode of a main electrode is easily dissolved, and if it is higher than 70 Hz, it is easily affected by the components of inductance in a power supply circuit, thus the electric power cost increases.

Examples of the power supply which may be used include a commercial alternating current which is phase angle-controlled with a thyristor, a commercial alternating current which is controlled with a saturable reactor, an inverter-controlled power supply, and a PWM-controlled power supply. It is preferable in view of the cost and controllability to use a PWM-controlled power supply.

FIG. 4 is a schematic view of a radial electrolytic cell such as may be employed to carry out the electrochemical graining treatment using alternating current in the method of manufacturing a lithographic printing plate support according to the present invention.

One or more AC power supplies may be connected to the electrolytic cell. To control the anode/cathode current ratio of the alternating current applied to the aluminum plate opposite the main electrodes and thereby carry out uniform graining and to dissolve carbon from the main electrodes, it is advantageous to provide an auxiliary anode and divert some of the alternating current, as shown in FIG. 4. FIG. 4 shows an aluminum plate 11, a radial drum roller 12, main electrodes 13 a and 13 b, an electrolytic treatment solution 14, a solution feed inlet 15, a slit 16, a solution channel 17, an auxiliary anode 18, thyristors 19 a and 19 b, an AC power supply 20, a main electrolytic cell 21 and an auxiliary anode cell 22. By using a rectifying or switching device to divert some of the current as direct current to the auxiliary anode provided in the separate cell from that containing the two main electrodes, it is possible to control the ratio between the values of the current used for the anodic reaction on the aluminum plate opposite the main electrodes and the current used for the cathodic reaction on the aluminum plate. The ratio between the amount of electricity used for the anodic reaction and that used for the cathodic reaction, with both reactions occurring on the aluminum plate opposite the main electrodes, (amount of electricity on cathode/amount of electricity on anode) is preferably 0.3 to 0.95.

Any known electrolytic cell employed for surface treatment, including vertical, flat and radial type electrolytic cells, may be used in the method of manufacturing a lithographic printing plate support of the present invention. Radial-type electrolytic cells such as described in JP 5-195300 A are especially preferred. The electrolyte solution passes through the electrolytic cell either parallel or counter to the direction in which the aluminum web advances.

If the electrochemical graining treatment is performed using direct current, the electrolyte solution may be that employed for the conventional electrochemical graining treatment using direct current. Specifically, any electrolyte solution for the electrochemical graining treatment using alternating current as described above is applicable.

No particular limitation is imposed on the DC power supply waves used in the electrochemical graining treatment as long as they are of an electric current which is not changed in polarity. Comb-like waves, a continuous direct current, a direct current obtained by full-wave rectification of a commercial alternating current with thyristors, or the like may be used. Preferred is a continuous direct current which is obtained by smoothing.

The electrochemical graining treatment using direct current may be performed in batches, semicontinuously, or continuously. A continuous method is preferable.

Following completion of the first hydrochloric acid electrolysis, it is desirable to remove the solution from the aluminum plate with nip rollers, rinse the plate with water for 1 to 10 seconds, then remove the water with nip rollers.

Rinsing treatment is preferably carried out using a spray line. The spray line used in rinsing treatment is typically one having a plurality of spray tips disposed along the width of the aluminum plate, each of which discharges a fanned-out spray of water. The interval between the spray tips is preferably 20 to 100 mm, and the amount of water discharged per spray tip is preferably 1 to 20 L/min. The use of a plurality of spray lines is preferred.

The average aperture diameter of the recesses (pits) formed by the first hydrochloric acid electrolysis is measured as follows, for instance: The surface of a support is photographed at a magnification of 2,000 or 50,000 from right above with an electron microscope. Next, in each of the electron micrographs obtained, at least 50 pits whose circumferences are annularly combined are extracted, the diameter of the pits is read as the aperture diameter to calculate the average aperture diameter.

In order to suppress the dispersion of measurements, equivalent circle diameter measurement may be performed with packaged image analysis software. In that case, the aforementioned electron micrographs are read with a scanner and the data thus obtained are digitized by binary coding with the software to find the equivalent circle diameter.

In the measurement by the present inventors, the results of actual measurement were well conformed to those of digital processing.

The average surface roughness R_(a) of the aluminum plate after the first hydrochloric acid electrolysis is measured by the same method as used for the measurement after the mechanical graining treatment as described before. Specifically: Two-dimensional roughness measurement is conducted using a stylus-type roughness tester. The average roughness R_(a) as defined in ISO 4287 is measured five times, and the mean of the five measurements is used as the value of the average surface roughness.

<Second Alkali Etching Treatment>

In the present invention, it is preferable to perform, after the first hydrochloric acid electrolysis, a second alkali etching treatment for etching the surface of the aluminum plate in an aqueous alkali solution.

The purpose of the second alkali etching treatment performed between the first and second hydrochloric acid electrolyses is to dissolve smut that arises in the first hydrochloric acid electrolysis and to dissolve the edges of the pits formed by the first hydrochloric acid electrolysis. The present step dissolves the edges of the large pits formed by the first hydrochloric acid electrolysis, smoothing the surface and discouraging ink from catching on such edges. As a result, presensitized plates of excellent scumming resistance can be obtained.

The second alkali etching treatment is basically the same as the first alkali etching treatment so that only differences are to be explained below.

In the second alkali etching treatment, the etching amount is preferably at least 0.01 g/m², more preferably at least 0.1 g/m² and even more preferably at least 0.2 g/m², but preferably not more than 3 g/m², more preferably not more than 1.5 g/m² and even more preferably not more than 1.0 g/m². If the etching amount is 0.01 g/m² or more, the edges of the pits formed by the first hydrochloric acid electrolysis so get smooth that ink hardly catches on the edges, which improves the scumming resistance in the non-image area of a lithographic printing plate. On the other hand, an etching amount of 3 g/m² or less makes the press life better because the asperities provided by the first hydrochloric acid electrolysis are not decreased.

The concentration of the alkali solution used in the second alkali etching treatment is preferably at least 30 g/L and more preferably at least 40 g/L, but preferably not more than 500 g/L and more preferably not more than 450 g/L.

The alkali solution preferably contains aluminum ions. The aluminum ion concentration is preferably at least 1 g/L and more preferably at least 3 g/L, but preferably not more than 200 g/L and more preferably not more than 150 g/L. Such an alkali solution may be prepared by using water, a 48 wt % aqueous solution of sodium hydroxide, and sodium aluminate, for instance.

<Second Desmutting Treatment>

After the second alkali etching treatment has been carried out, it is preferable to carry out acid pickling (second desmutting treatment) to remove contaminants (smut) remaining on the surface of the aluminum plate. The second desmutting treatment may be carried out in the same way as the first desmutting treatment.

In the second desmutting treatment, it is preferable to use nitric acid or sulfuric acid.

An acidic solution containing 1 to 400 g/L of an acid and 0.5 to 8 g/L of aluminum ions may suitably be used in the second desmuttng treatment.

Specifically, in the case of using sulfuric acid, the solution to be used may be prepared by dissolving aluminum sulfate in a 100 to 350 g/L aqueous solution of sulfuric acid to allow an aluminum ion concentration of 0.1 to 5 g/L. It is also possible to use an overflow waste of the electrolyte solution used in an anodizing treatment as will be described later.

In the second desmutting treatment, the treatment time is preferably at least 1 second, and more preferably at least 4 seconds, but preferably not more than 60 seconds, and more preferably not more than 20 seconds.

The temperature of the acidic solution used in the second desmutting treatment is preferably at least 20° C., and more preferably at least 30° C., but preferably not more than 70° C., and more preferably not more than 60° C.

<Second Hydrochloric Acid Electrolysis>

In the present invention, it is preferable to perform, after the second alkali etching treatment or the second desmutting treatment, a second hydrochloric acid electrolysis for electrochemically graining in an aqueous solution containing hydrochloric acid.

The second hydrochloric acid electrolysis is an electrochemical graining treatment which is performed in an aqueous solution containing hydrochloric acid using alternating or direct current. According to the present invention combining the second hydrochloric acid electrolysis with the first hydrochloric acid electrolysis as described before, the surface of the aluminum plate can be so grained as to have a complex profile as a result of the superimposition of different types of asperities of a high uniformity, enabling a higher scumming resistance, a better press life and further an excellent cleaner resistance to be achieved.

Moreover, pits with an average aperture diameter of 0.01 to 0.4 μm can be formed by the second hydrochloric acid electrolysis on the aluminum surface once smoothed by the second alkali etching, which also contributes to the improvement of the press life.

The second hydrochloric acid electrolysis, as being performed after the first hydrochloric acid electrolysis, is basically similar to the first one.

The aqueous solution containing hydrochloric acid that is to be used in the second hydrochloric acid electrolysis may be any such solution as used in conventional electrochemical graining treatments employing direct or alternating current, as is the case with the first hydrochloric acid electrolysis. A desirable solution is an aqueous solution of hydrochloric acid with a concentration of 1 to 30 g/L, preferably 3 to 20 g/L, and more preferably 6 to 15 g/L. The solution may also contain 0.1 to 10 g/L of sulfate ions or nitrate ions.

In the electrochemical graining in an aqueous solution containing hydrochloric acid that is carried out by the second hydrochloric acid electrolysis, the total amount of electricity used for the anodic reaction on the aluminum plate is preferably 10 to 300 C/dm², more preferably 30 to 150 C/dm², and further preferably 50 to 100 C/dm², at the end of the electrochemical graining.

As for the value of the total amount of electricity used for the anodic reaction, it is preferable that a value Q₁ used by the end of electrolytic reaction in the first hydrochloric acid electrolysis is larger than a value Q₂ used by the end of electrolytic reaction in the second hydrochloric acid electrolysis (Q₁>Q₂). Under such conditions, the pits with an average aperture diameter of 1 to 15 μm formed by the first hydrochloric acid electrolysis are allowed to have an increased surface area, resulting in a larger surface area of the aluminum plate. Adhesion between the aluminum plate and an image recording layer formed thereon is thus improved and the press life as well.

<Third Alkali Etching Treatment>

In the present invention, it is preferable to perform, after the second hydrochloric acid electrolysis, a third alkali etching treatment for etching the surface of the aluminum plate in an aqueous alkali solution.

The purpose of the third alkali etching treatment performed after the second hydrochloric acid electrolysis is to dissolve smut that arises in the second hydrochloric acid electrolysis and to dissolve the edges of the pits formed by the second hydrochloric acid electrolysis. The third alkali etching treatment is basically the same as the first alkali etching treatment so that only differences are to be explained below.

In the third alkali etching treatment, the etching amount is preferably at least 0.05 g/m² and more preferably at least 0.1 g/m², but preferably not more than 0.5 g/m² and more preferably not more than 0.3 g/m². If the etching amount is 0.05 g/m² or more, the edges of the pits formed by the second hydrochloric acid electrolysis so get smooth that ink hardly catches on the edges, which improves the scumming resistance in the non-image area of a lithographic printing plate. On the other hand, an etching amount of 0.5 g/m² or less makes the press life better because the pits of a 0.01 to 0.4 μm average diameter formed by the hydrochloric acid electrolysis are kept intact.

The concentration of the alkali solution used in the third alkali etching treatment is preferably at least 30 g/L. In order to avoid a too much reduction in the depth of the recesses formed by the former hydrochloric acid electrolysis, however, the concentration is preferably not more than 100 g/L and more preferably not more than 70 g/L.

The alkali solution preferably contains aluminum ions. The aluminum ion concentration is preferably at least 1 g/L and more preferably at least 3 g/L, but preferably not more than 50 g/L and more preferably not more than 8 g/L. Such an alkali solution may be prepared by using water, a 48 wt % aqueous solution of sodium hydroxide, and sodium aluminate, for instance.

In the third alkali etching treatment, the temperature of the alkali solution is preferably at least 25° C. and more preferably at least 30° C., but preferably not more than 60° C. and more preferably not more than 50° C.

The treatment time for the third alkali etching treatment is preferably at least 1 second and more preferably at least 2 seconds, but preferably not more than 30 seconds and more preferably not more than 10 seconds.

<Third Desmutting Treatment>

After the third etching treatment has been carried out, it is preferable to carry out acid pickling (third desmutting treatment) to remove contaminants (smut) remaining on the surface of the aluminum plate. The third desmutting treatment is basically the same as the first desmutting treatment so that only differences are to be explained below.

In the third desmutting treatment, it is preferable to use a solution of the same type as the electrolyte solution (sulfuric acid, for instance) used in the anodizing treatment to be subsequently performed because a rinsing process between the third desmutting treatment and the anodizing treatment can then be omitted.

The solution used in the third desmutting treatment is preferably an acidic solution containing 5 to 400 g/L of an acid and 0.5 to 8 g/L of aluminum ions. Specifically, in the case of using sulfuric acid, a preferable solution may be prepared by dissolving aluminum sulfate in a 100 to 350 g/L aqueous solution of sulfuric acid to allow an aluminum ion concentration of 1 to 5 g/L.

The treatment time for the third desmutting treatment is preferably at least 1 second, and more preferably at least 4 seconds, but preferably not more than 60 seconds, and more preferably not more than 15 seconds.

If the desmutting treatment solution used in the third desmutting treatment is a solution of the same type as the electrolyte solution used in the anodizing treatment to be subsequently performed, removal of the solution with nip rollers and rinsing may not be performed on the plate after the desmutting treatment.

<Anodizing Treatment>

The aluminum plate treated as described above is further subjected to anodizing treatment. Anodizing treatment can be carried out by any suitable method used in the field to which the present invention pertains. More specifically, an anodized layer can be formed on the aluminum plate surface by, for example, passing a current through the aluminum plate as an anode in a solution having a sulfuric acid concentration of 50 to 300 g/L and an aluminum concentration of up to 5 wt %. The solution used for anodizing treatment may include sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid or the like alone or in combination.

In this connection, components ordinarily present in at least the aluminum plate, electrodes, tap water, ground water and the like are acceptable in the electrolyte solution. In addition, secondary and tertiary components may be added. Examples of the “secondary and tertiary components” include ions of such a metal as sodium, potassium, magnesium, lithium, calcium, titanium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc; cations such as ammonium ions; and anions such as nitrate ions, carbonate ions, chloride ions, phosphate ions, fluoride ions, sulfite ions, titanate ions, silicate ions and borate ions. These may be present in a concentration of about 0 to 10,000 ppm.

The anodizing treatment conditions vary empirically according to the electrolyte solution used, although it is generally suitable for the electrolyte solution to have a concentration of 1 to 80 wt % and a temperature of 5 to 70° C., and for the current density to be 0.5 to 60 A/dm², the voltage to be 1 to 100 V, and the electrolysis time to be 15 seconds to 50 minutes. These conditions may be adjusted to obtain the desired anodized layer weight.

Methods that may be used to carry out anodizing treatment include those described in JP 54-81133 A, JP 57-47894 A, JP 57-51289 A, JP 57-51290 A, JP 57-54300 A, JP 57-136596 A, JP 58-107498 A, JP 60-200256 A, JP 62-136596 A, JP 63-176494 A, JP 4-176897 A, JP 4-280997 A, JP 6-207299 A, JP 5-24377 A, JP 5-32083 A, JP 5-125597 A and JP 5-195291 A.

Among others, it is preferable to use a sulfuric acid solution as the electrolyte solution, as described in JP 54-12853 A and JP 48-45303 A. The solution has a sulfuric acid concentration of preferably 10 to 300 g/L (1 to 30 wt %), and more preferably 50 to 200 g/L (5 to 20 wt %), and an aluminum ion concentration of preferably 1 to 25 g/L (0.1 to 2.5 wt %), and more preferably 2 to 10 g/L (0.2 to 1 wt %). Such an electrolyte solution can be prepared by, for instance, adding aluminum sulfate to a dilute sulfuric acid having a sulfuric acid concentration of 50 to 200 g/L.

Control of the electrolyte solution composition is preferably carried out using a method similar to that employed in the nitric acid electrolysis as described before. That is, the composition may be controlled based on the electrical conductivity, specific gravity and temperature, or on the electrical conductivity, ultrasonic wave propagation velocity and temperature, which parameters are corresponding to a matrix of the sulfuric acid concentration and the aluminum ion concentration.

The electrolyte solution has a temperature of preferably 25 to 55° C., and more preferably 30 to 50° C.

When anodizing treatment is carried out in an electrolyte solution containing sulfuric acid, direct current or alternating current may be applied across the aluminum plate and the counter electrode.

When a direct current is applied to the aluminum plate, the current density is preferably 1 to 60 A/dm², and more preferably 5 to 40 A/dm².

To keep burnt deposits (areas of the anodized layer which are thicker than surrounding areas) from arising on portions of the aluminum plate due to the concentration of current when anodizing treatment is carried out as a continuous process, it is preferable to apply current at a low density of 5 to 10 A/dm² at the start of anodizing treatment and to increase the current density to 30 to 50 A/dm² or more as anodizing treatment proceeds.

Specifically, it is preferable for current from the DC power supplies to be allocated such that current from downstream DC power supplies is equal to or greater than current from upstream DC power supplies. Current allocation in this way will discourage the formation of burnt deposits, enabling high-speed anodization to be carried out.

When anodizing treatment is carried out as a continuous process, this is preferably done using a system that supplies power to the aluminum plate through the electrolyte solution.

By carrying out anodizing treatment under such conditions, a porous film with numerous micropores can be obtained. The film generally has an average pore diameter of about 5 to 50 nm and an average pore density of about 300 to 800 pores/μm².

The weight of the anodized layer is preferably 1 to 5 g/m². At a weight of less than 1 g/m², scratches are readily formed on the plate. A weight of more than 5 g/m² requires a large amount of electrical power for the formation of the layer, which is economically disadvantageous. An anodized layer weight of 1.5 to 4 g/m² is more preferred. It is also desirable for anodizing treatment to be carried out in such a way that the difference in the anodized layer weight between the center of the aluminum plate and the areas near the edges is not more than 1 g/m².

Examples of electrolyzing apparatuses that may be used in anodizing treatment include those described in JP 48-26638 A, JP 47-18739 A, JP 58-24517 B and JP 2001-11698 A.

Among others, an apparatus like that shown in FIG. 5 is preferred. FIG. 5 is a schematic view showing an exemplary apparatus for anodizing the surface of an aluminum plate.

In an anodizing apparatus 410 shown in FIG. 5, to apply a current to an aluminum plate 416 through an electrolyte solution, a power supplying cell 412 is disposed upstream in the direction of advance of the aluminum plate 416 and an anodizing treatment tank 414 downstream. The aluminum plate 416 is moved by path rollers 422 and 428 in the direction indicated by the arrows in FIG. 5. The power supplying cell 412 through which the aluminum plate 416 first passes is provided with anodes 420 which are connected to the positive poles of a DC power supply 434, and the aluminum plate 416 serves as the cathode in the cell. Hence, a cathodic reaction arises at the aluminum plate 416.

The anodizing treatment tank 414 through which the aluminum plate 416 next passes is provided with a cathode 430 which is connected to the negative pole of the DC power supply 434, and the aluminum plate 416 serves as the anode in the tank. Hence, an anodic reaction arises at the aluminum plate 416, and an anodized layer is formed on the surface of the aluminum plate 416.

The aluminum plate 416 is at a distance of preferably 50 to 200 mm from the cathode 430. The cathode 430 is made of aluminum. To facilitate the venting of hydrogen gas generated by the anodic reaction from the system, it is preferable for the cathode 430 to be divided into a plurality of sections in the direction of advance of the aluminum plate 416 rather than to be a single electrode having a broad surface area.

As shown in FIG. 5, it is advantageous to provide, between the power supplying cell 412 and the anodizing treatment tank 414, an intermediate tank 413 that does not hold the electrolyte solution. By providing the intermediate tank 413, the current can be kept from passing directly from the anode 420 to the cathode 430 and bypassing the aluminum plate 416. It is preferable to minimize the bypass current by providing nip rollers 424 in the intermediate tank 413 to remove the solution from the aluminum plate 416. The electrolyte solution removed by the nip rollers 424 is discharged outside the anodizing apparatus 410 through a discharge outlet 442.

To lower the voltage loss, an electrolyte solution 418 contained in the power supplying cell 412 is set at a higher temperature and/or concentration than an electrolyte solution 426 contained in the anodizing treatment tank 414. Moreover, the composition, temperature and other characteristics of the electrolyte solutions 418 and 426 are set based on such considerations as the anodized layer forming efficiency, the shapes of micropores in the anodized layer, the hardness of the anodized layer, the voltage, and the cost of the electrolyte solution.

The power supplying cell 412 and the anodizing treatment tank 414 are supplied with electrolyte solutions injected by solution feed nozzles 436 and 438. To ensure that the distribution of electrolyte solution remains uniform and thereby prevent the localized concentration of current on the aluminum plate 416 in the anodizing treatment tank 414, the solution feed nozzles 436 and 438 have a construction in which slits are provided to keep the flow of injected liquid constant in the width direction.

In the anodizing treatment tank 414, a shield 440 is provided on the opposite side of the aluminum plate 416 from the cathode 430 to check the flow of current to the opposite surface of the aluminum plate 416 with the surface on which an anodized layer is to be formed. The interval between the aluminum plate 416 and the shield 440 is preferably 5 to 30 mm. It is preferable to use a plurality of DC power supplies as the DC power supply 434, with their positive poles being connected in common, thereby enabling control of the current distribution within the anodizing treatment tank 414.

<Sealing Treatment>

Sealing treatment may be carried out as required to seal micropores in the anodized layer. Such treatment can enhance the developability (sensitivity) of the presensitized plate.

Anodized layers are known to be porous films having micropores which extend in a direction substantially perpendicular to the surface of the film. In the present invention, it is advantageous to carry out sealing treatment to a high sealing ratio following the anodizing treatment. The sealing ratio is preferably at least 50%, more preferably at least 70%, and even more preferably at least 90%. “Sealing ratio,” as used herein, is defined as follows. Sealing ratio=[(surface area before sealing)−(surface area after sealing)]/(surface area before sealing)×100%

The surface area can be measured using a simple BET-type surface area analyzer, such as Quantasorb (Yuasa Ionics Inc.).

Sealing may be carried out using any known method without particular limitation. Illustrative examples of sealing methods that may be used include hot water treatment, boiling water treatment, steam treatment, dichromate treatment, nitrite treatment, ammonium acetate treatment, electrodeposition sealing treatment, hexafluorozirconic acid treatment like that described in JP 36-22063 B, treatment with an aqueous solution containing a phosphate and an inorganic fluorine compound as described in JP 9-244227 A, treatment with a sugar-containing aqueous solution as described in JP 9-134002 A, treatment with a titanium and fluorine-containing aqueous solution as described in JP 2000-81704 A and JP 2000-89466 A, and alkali metal silicate treatment like that described in U.S. Pat. No. 3,181,461.

One preferred type of sealing treatment is alkali metal silicate treatment. This can be carried out using a pH 10 to 13 aqueous solution of an alkali metal silicate at 25° C. that does not undergo solution gelation or dissolve the anodized layer, and by suitably selecting the treatment conditions, such as the alkali metal silicate concentration, the treatment temperature and the treatment time. Preferred alkali metal silicates include sodium silicate, potassium silicate and lithium silicate. Sodium hydroxide, potassium hydroxide, lithium hydroxide or the like may be incorporated in the aqueous solution of alkali metal silicate in order to increase the pH thereof.

If necessary, an alkaline earth metal salt and/or a Group 4 (Group IVA) metal salt may also be included in the aqueous alkali metal silicate solution. Examples of suitable alkaline earth metal salts include the following water-soluble salts: nitrates such as calcium nitrate, strontium nitrate, magnesium nitrate and barium nitrate; and also sulfates, hydrochlorides, phosphates, acetates, oxalates, and borates of alkaline earth metals. Exemplary Group 4 (Group IVA) metal salts include titanium tetrachloride, titanium trichloride, titanium potassium fluoride, titanium potassium oxalate, titanium sulfate, titanium tetraiodide, zirconyl chloride, zirconium dioxide and zirconium tetrachloride. These alkaline earth metal salts and Group 4 (Group IVA) metal salts may be used singly or in combinations of two or more thereof.

The concentration of the aqueous alkali metal silicate solution is preferably 0.01 to 10 wt %, and more preferably 0.05 to 5.0 wt %.

Another preferred type of sealing treatment is hexafluorozirconic acid treatment. Such treatment is carried out using a hexafluorozirconate such as sodium hexafluorozirconate and potassium hexafluorozirconate. It is particularly preferable to use sodium hexafluorozirconate. This treatment provides the presensitized plate with excellent developability (sensitivity). The hexafluorozirconate solution used in this treatment has a concentration of preferably 0.01 to 2 wt %, and more preferably 0.1 to 0.3 wt %.

It is desirable for the hexafluorozirconate solution to contain sodium dihydrogenphosphate in a concentration of preferably 0.01 to 3 wt %, and more preferably 0.1 to 0.3 wt %.

The hexafluorozirconate solution may contain aluminum ions. In this case, the hexafluorozirconate-solution has preferably an aluminum ion concentration of 1 to 500 mg/L.

The sealing treatment temperature is preferably 20 to 90° C., and more preferably 50 to 80° C.

The sealing treatment time (period of immersion in the solution) is preferably 1 to 20 seconds, and more preferably 5 to 15 seconds.

If necessary, sealing treatment may be followed by surface treatment such as the above-described alkali metal silicate treatment or treatment in which the aluminum plate is immersed in or coated with a solution containing polyvinylphosphonic acid, polyacrylic acid, a polymer or copolymer having pendant groups such as sulfo groups, or any of the organic compounds, or salts thereof, as described in JP 11-231509 A which has an amino group and a phosphine group, phosphone group or phosphoric acid group.

Following sealing treatment, it is desirable to carry out the hydrophilizing treatment described below.

<Hydrophilizing Treatment>

Hydrophilizing treatment may be carried out after anodizing treatment or sealing treatment. Illustrative examples of suitable hydrophilizing treatments include the potassium hexafluorozirconate treatment described in U.S. Pat. No. 2,946,638, the phosphomolybdate treatment described in U.S. Pat. No. 3,201,247, the alkyl titanate treatment described in GB 1,108,559, the polyacrylic acid treatment described in DE 1,091,433, the polyvinylphosphonic acid treatments described in DE 1,134,093 and GB 1,230,447, the phosphonic acid treatment described in JP 44-6409 B, the phytic acid treatment described in U.S. Pat. No. 3,307,951, the treatments involving the divalent metal salt of a lipophilic organic polymeric compound described in JP 58-16893 A and JP 58-18291 A, a treatment like that described in U.S. Pat. No. 3,860,426 in which an undercoat of a hydrophilic cellulose (e.g., carboxymethyl cellulose) containing a water-soluble metal salt (e.g., zinc acetate) is provided, and the treatment as described in JP 59-101651 A in which a sulfo group-bearing water-soluble polymer is undercoated.

Additional examples of suitable hydrophilizing treatments include undercoating treatment using the phosphates described in JP 62-019494 A, the water-soluble epoxy compounds described in JP 62-033692 A, the phosphoric acid-modified starches described in JP 62-097892 A, the diamine compounds described in JP 63-056498 A, the inorganic or organic salts of amino acids described in JP 63-130391 A, the carboxy or hydroxy group-bearing organic phosphonic acids described in JP 63-145092 A, the amino group and phosphonic acid group-bearing compounds described in JP 63-165183 A, the specific carboxylic acid derivatives described in JP 2-316290 A, the phosphate esters described in JP 3-215095 A, the compounds having one amino group and one phosphorus oxoacid group described in JP 3-261592 A, the aliphatic or aromatic phosphonic acids (e.g., phenylphosphonic acid) described in JP 5-246171 A, the sulfur atom-bearing compounds (e.g., thiosalicylic acid) described in JP 1-307745 A, and the phosphorus oxoacid group-bearing compounds described in JP 4-282637 A.

Coloration with an acid dye as described in JP 60-64352 A may also be carried out.

It is preferable to carry out hydrophilizing treatment by a method in which the aluminum plate is immersed in an aqueous solution of an alkali metal silicate such as sodium silicate or potassium silicate, or is coated with a hydrophilic vinyl polymer or some other hydrophilic compound so as to form a hydrophilic undercoat.

Hydrophilizing treatment with an aqueous solution of an alkali metal silicate such as sodium silicate or potassium silicate can be carried out according to the processes and procedures described in U.S. Pat. No. 2,714,066 and U.S. Pat. No. 3,181,461.

Illustrative examples of suitable alkali metal silicates include sodium silicate, potassium silicate and lithium silicate. Suitable amounts of sodium hydroxide, potassium hydroxide, lithium hydroxide or the like may be included in the aqueous alkali metal silicate solution.

An alkaline earth metal salt or a Group 4 (Group IVA) metal salt may also be included in the aqueous alkali metal silicate solution. Examples of suitable alkaline earth metal salts include nitrates such as calcium nitrate, strontium nitrate, magnesium nitrate and barium nitrate; and also sulfates, hydrochlorides, phosphates, acetates, oxalates, and borates. Exemplary Group 4 (Group IVA) metal salts include titanium tetrachloride, titanium trichloride, titanium potassium fluoride, titanium potassium oxalate, titanium sulfate, titanium tetraiodide, zirconyl chloride, zirconium dioxide and zirconium tetrachloride. These alkaline earth metal salts and Group 4 (Group IVA) metal salts may be used singly or in combinations of two or more thereof.

The amount of silicon adsorbed as a result of alkali metal silicate treatment can be measured with a fluorescent x-ray analyzer, and is preferably about 1.0 to 15.0 mg/m².

This alkali metal silicate treatment has the effect of enhancing the resistance at the surface of the lithographic printing plate support to dissolution by the alkaline developer, suppressing the leaching of aluminum ingredients into the developer, and reducing the generation of development scum due to developer fatigue.

Hydrophilizing treatment involving the formation of a hydrophilic undercoat can also be carried out in accordance with the conditions and procedures described in JP 59-101651 A and JP 60-149491 A.

Hydrophilic vinyl polymers that may be used in such a method include copolymers of a sulfo group-bearing vinyl polymerizable compound such as polyvinylsulfonic acid or sulfo group-bearing p-styrenesulfonic acid with a conventional vinyl polymerizable compound such as an alkyl (meth)acrylate. Examples of hydrophilic compounds that may be used in this method include compounds having at least one group selected from among —NH₂ groups, —COOH groups and sulfo groups.

<Drying>

After the lithographic printing plate support has been obtained as described above, it is advantageous to dry the surface of the support before providing an image recording layer thereon. Drying is preferably carried out after the support has been rinsed with water and the water removed with nip rollers following the final surface treatment.

The drying temperature is preferably at least 70° C., and more preferably at least 80° C., but preferably not more than 110° C., and more preferably not more than 100° C.

The drying time is preferably at least 1 second, and more preferably at least 2 seconds, but preferably not more than 20 seconds, and more preferably not more than 15 seconds.

<Control of Solution Composition>

In the present invention, it is preferable to control the composition of various treatment solutions used in the surface treatments as described above by the method as disclosed in JP 2001-121837 A. The solution composition may be measured by ion chromatography, capillary electrophoresis, and so forth.

It should be noted that the Cu concentration of the electrolyte solutions used in the electrolytic graining treatments and anodizing treatment as above is preferably not more than 100 ppm. With a higher Cu concentration, Cu may be deposited on the aluminum plate during the stop of production line and the deposited Cu may be transferred to path rollers when the line is brought into operation again, causing treatment irregularities.

[Presensitized Plate]

The lithographic printing plate support according to the present invention can be formed into a presensitized plate of the present invention by providing an image recording layer thereon. A photosensitive composition is used in the image recording layer.

Preferred examples of photosensitive compositions that may be used in the present invention include thermal positive-type photosensitive compositions containing an alkali-soluble polymeric compound and a photothermal conversion substance (such compositions and the image recording layers obtained using these compositions are referred to below as “thermal positive-type” compositions and image recording layers), thermal negative-type photosensitive compositions containing a curable compound and a photothermal conversion substance (these compositions and the image recording layers obtained therefrom are similarly referred to below as “thermal negative-type” compositions and image recording layers), photopolymerizable photosensitive compositions (referred to below as “photopolymer-type” compositions), negative-type photosensitive compositions containing a diazo resin or a photo-crosslinkable resin (referred to below as “conventional negative-type” compositions), positive-type photosensitive compositions containing a quinonediazide compound (referred to below as “conventional positive-type” compositions), and photosensitive compositions that do not require a special development step (referred to below as “non-treatment type” compositions). The thermal positive-type, thermal negative-type and non-treatment type compositions are particularly preferred. These preferred photosensitive compositions are described below.

<Thermal Positive-Type Photosensitive Compositions>

<Photosensitive Layer>

Thermal positive-type photosensitive compositions contain an alkali-soluble polymeric compound and a photothermal conversion substance. In a thermal positive-type image recording layer, the photothermal conversion substance converts light energy such as from an infrared laser into heat, which efficiently eliminates interactions that lower the alkali solubility of the alkali-soluble polymeric compound.

The alkali-soluble polymeric compound may be, for example, a resin having an acidic group on the molecule, or a mixture of two or more such resins. Resins having an acidic group, such as a phenolic hydroxy group, a sulfonamide group (—SO₂NH—R, wherein R is a hydrocarbon group) or an active imino group (—SO₂NHCOR, —SO₂NHSO₂R or —CONHSO₂R, wherein R is as defined above), are especially preferred on account of their solubility in alkaline developers.

For an excellent image formability with exposure to light from an infrared laser, for example, resins having phenolic hydroxy groups are especially desirable. Preferred examples of such resins include novolak resins such as phenol-formaldehyde resins, m-cresol-formaldehyde resins, p-cresol-formaldehyde resins, cresol-formaldehyde resins in which the cresol is a mixture of m-cresol and p-cresol, and phenol/cresol mixture-formaldehyde resins (phenol-cresol-formaldehyde co-condensation resins) in which the cresol is m-cresol, p-cresol or a mixture of m- and p-cresol.

Additional preferred examples include the polymeric compounds described in JP 2001-305722 A (especially paragraphs to [0042]), the polymeric compounds having recurring units of general formula (1) described in JP 2001-215693 A, and the polymeric compounds described in JP 2002-311570 A (especially paragraph [0107]).

To provide a good recording sensitivity, the photothermal conversion substance is preferably a pigment or dye that absorbs light in the infrared wavelength range of 700 to 1200 nm. Illustrative examples of suitable dyes include azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinoneimine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrylium salts and metal-thiolate complexes (e.g., nickel-thiolate complexes). Of these, cyanine dyes are preferred. The cyanine dyes of general formula (I) described in JP 2001-305722 A are especially preferred.

A dissolution inhibitor may be included in thermal positive-type photosensitive compositions. Preferred examples of dissolution inhibitors include those described in paragraphs [0053] to [0055] of JP 2001-305722 A.

The thermal positive-type photosensitive compositions preferably also include, as additives, sensitivity regulators, print-out agents for obtaining a visible image immediately after heating from light exposure, compounds such as dyes as image colorants, and surfactants for enhancing coatability and treatment stability. Compounds such as described in paragraphs [0056] to [0060] of JP 2001-305722 A are preferred additives.

Use of the photosensitive compositions described in detail in JP 2001-305722 A is desirable because of the above preferred components and additional advantages.

The thermal positive-type image recording layer is not limited to a single layer, but may have a two-layer construction.

Preferred examples of image recording layers with a two-layer construction (also referred to as “multilayer-type image recording layers”) include those comprising a bottom layer (“layer A”) of excellent press life and solvent resistance which is provided on the side close to the support and a layer (“layer B”) having an excellent positive-image formability which is provided on layer A. This type of image recording layer has a high sensitivity and can provide a broad development latitude. Layer B generally contains a photothermal conversion substance. Preferred examples of the photothermal conversion substance include the dyes mentioned above.

Preferred examples of resins that may be used in layer A include polymers that contain as a copolymerizable component a monomer having a sulfonamide group, an active imino group or a phenolic hydroxy group; such polymers have an excellent press life and solvent resistance. Preferred examples of resins that may be used in layer B include phenolic hydroxy group-bearing resins which are soluble in aqueous alkali solutions.

In addition to the above resins, various additives may be included, if necessary, in the compositions used to form layers A and B. For example, suitable use can be made of the additives described in paragraphs [0062] to [0085] of JP 2002-323769 A. The additives described in paragraphs [0053] to [0060] of JP 2001-305722 A as above are also suitable for use.

The components and proportions thereof in each of layers A and B are preferably selected as described in JP 11-218914 A.

<Intermediate Layer>

It is advantageous to provide an intermediate layer between the thermal positive-type image recording layer and the support. Preferred examples of ingredients that may be used in the intermediate layer include the various organic compounds described in paragraph [0068] of JP 2001-305722 A.

<Others>

The methods described in detail in JP 2001-305722 A may be used to form a thermal positive-type image recording layer and to make a printing plate having such a layer.

<Thermal Negative-Type Photosensitive Compositions>

Thermal negative-type photosensitive compositions contain a curable compound and a photothermal conversion substance. A thermal negative-type image recording layer is a negative-type photosensitive layer in which areas irradiated with light such as from an infrared laser cure to form image areas.

<Polymerizable Layer>

An example of a preferred thermal negative-type image recording layer is a polymerizable image recording layer (polymerizable layer). The polymerizable layer contains a photothermal conversion substance, a radical generator, a radical-polymerizable compound which is a curable compound, and a binder polymer. In the polymerizable layer, the photothermal conversion substance converts absorbed infrared light into heat, and the heat decomposes the radical generator, thereby generating radicals. The radicals then trigger the chain polymerization and curing of the radical-polymerizable compound.

Illustrative examples of the photothermal conversion substance include photothermal conversion substances that may be used in the above-described thermal positive-type photosensitive compositions. Specific examples of cyanine dyes, which are especially preferred, include those described in paragraphs [0017] to [0019] of JP 2001-133969 A.

Preferred radical generators include onium salts. The onium salts described in paragraphs [0030] to [0033] of JP 2001-133969 A are especially preferred.

Exemplary radical-polymerizable compounds include compounds having one, and preferably two or more, terminal ethylenically unsaturated bonds.

Preferred binder polymers include linear organic polymers. Linear organic polymers which are soluble or swellable in water or a weak alkali solution in water are preferred. Of these, (meth)acrylic resins having unsaturated groups (e.g., allyl, acryloyl) or benzyl groups and carboxy groups in side chains are especially preferred because they provide an excellent balance of film strength, sensitivity and developability.

Radical-polymerizable compounds and binder polymers that may be used include those described specifically in paragraphs [0036] to [0060] of JP 2001-133969 A.

Thermal negative-type photosensitive compositions preferably contain additives described in paragraphs [0061] to [0068] of JP 2001-133969 A (e.g., surfactants for enhancing coatability).

The methods described in detail in JP 2001-133969 A may be used to form a polymerizable layer and to make a printing plate having such a layer.

<Acid-Crosslinkable Layer>

Another preferred thermal negative-type image recording layer is an acid-crosslinkable image recording layer (abbreviated hereinafter as “acid-crosslinkable layer”). An acid-crosslinkable layer contains a photothermal conversion substance, a thermal acid generator, a compound (crosslinker) which is curable and which crosslinks under the influence of an acid, and an alkali-soluble polymeric compound which is capable of reacting with the crosslinker in the presence of an acid. In an acid-crosslinkable layer, the photothermal conversion substance converts absorbed infrared light into heat. The heat decomposes the thermal acid generator, thereby generating an acid which causes the crosslinker and the alkali-soluble polymeric compound to react and cure.

The photothermal conversion substance is exemplified by the same substances as can be used in the polymerizable layer.

Exemplary thermal acid generators include photoinitiators for photopolymerization, dye photochromogenic substances, and heat-decomposable compounds such as acid generators which are used in microresists and the like.

Exemplary crosslinkers include hydroxymethyl- or alkoxymethyl-substituted aromatic compounds, compounds having N-hydroxymethyl, N-alkoxymethyl or N-acyloxymethyl groups, and epoxy compounds.

Exemplary alkali-soluble polymeric compounds include novolak resins and polymers having hydroxyaryl groups in side chains.

<Photopolymer-Type Photosensitive Compositions>

Photopolymer-type photosensitive compositions contain an addition-polymerizable compound, a photopolymerization initiator and a polymer binder.

Preferred addition-polymerizable compounds include compounds containing an ethylenically unsaturated bond which are addition-polymerizable. Ethylenically unsaturated bond-containing compounds are compounds which have a terminal ethylenically unsaturated bond. Such compounds may have the chemical form of a monomer, a prepolymer, or a mixture thereof. The monomers are exemplified by esters of unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid, maleic acid) and aliphatic polyols, and amides of unsaturated carboxylic acids and aliphatic polyamines.

Preferred addition-polymerizable compounds include also urethane-type addition-polymerizable compounds.

The photopolymerization initiator may be any of various photopolymerization initiators or a system of two or more photopolymerization initiators (photoinitiation system) which is suitably selected according to the wavelength of the light source to be used. Preferred examples include the initiation systems described in paragraphs [0021] to [0023] of JP 2001-22079 A.

The polymer binder, inasmuch as it must function as a film-forming agent for the photopolymerizable photosensitive composition and, at the same time, must allow the image recording layer to dissolve in an alkaline developer, should be an organic polymer which is soluble or swellable in an aqueous alkali solution. Preferred examples of such organic polymers include those described in paragraphs [0036] to [0063] of JP 2001-22079 A.

It is preferable for the photopolymer-type photosensitive composition to include the additives described in paragraphs [0079] to [0088] of JP 2001-22079 A (e.g., surfactants for improving coatability, colorants, plasticizers, thermal polymerization inhibitors).

To prevent the inhibition of polymerization by oxygen, it is preferable to provide an oxygen-blocking protective layer on top of the photopolymer-type image recording layer. The polymer present in the oxygen-blocking protective layer is exemplified by polyvinyl alcohols and copolymers thereof.

It is also desirable to provide an intermediate layer or a bonding layer like those described in paragraphs [0124] to [0165] of JP 2001-228608 A.

<Conventional Negative-Type Photosensitive Compositions>

Conventional negative-type photosensitive compositions contain a diazo resin or a photo-crosslinkable resin. Among others, photosensitive compositions which contain a diazo resin and an alkali-soluble or -swellable polymeric compound (binder) are preferred.

The diazo resin is exemplified by condensation products of an aromatic diazonium salt with an active carbonyl group-bearing compound such as formaldehyde; and organic solvent-soluble diazo resin inorganic salts which are the reaction products of a hexafluorophosphate or tetrafluoroborate with the condensation product of a p-diazophenylamine and formaldehyde. The high-molecular-weight diazo compounds described in JP 59-78340 A, in which the content of hexamer and larger polymers is at least 20 mol %, are especially preferred.

Exemplary binders include copolymers containing acrylic acid, methacrylic acid, crotonic acid or maleic acid as an essential component. Specific examples include the multi-component copolymers of such monomers as 2-hydroxyethyl (meth)acrylate, (meth)acrylonitrile and (meth)acrylic acid described in JP 50-118802 A, and the multi-component copolymers of alkyl acrylates, (meth)acrylonitrile and unsaturated carboxylic acids described in JP 56-4144 A.

Conventional negative-type photosensitive compositions preferably contain as additives the print-out agents, dyes, plasticizers for imparting flexibility and wear resistance to the applied coat, development promoters and other compounds, and the surfactants for enhancing coatability described in paragraphs [0014] to [0015] of JP 7-281425 A.

Below the conventional negative-type photosensitive layer, it is advantageous to provide the intermediate layer which contains a polymeric compound having an acid group-bearing component and an onium group-bearing component described in JP 2000-105462 A.

<Conventional Positive-Type Photosensitive Compositions>

Conventional positive-type photosensitive compositions contain a quinonediazide compound. Photosensitive compositions containing an o-quinonediazide compound and an alkali-soluble polymeric compound are especially preferred.

Illustrative examples of the o-quinonediazide compound include esters of 1,2-naphthoquinone-2-diazido-5-sulfonylchloride and a phenol-formaldehyde resin or a cresol-formaldehyde resin, and the esters of 1,2-naphthoquinone-2-diazido-5-sulfonylchloride and pyrogallol-acetone resins described in U.S. Pat. No. 3,635,709.

Illustrative examples of the alkali-soluble polymeric compound include phenol-formaldehyde resins, cresol-formaldehyde resins, phenol-cresol-formaldehyde co-condensation resins, polyhydroxystyrene, N-(4-hydroxyphenyl)methacrylamide copolymers, the carboxy group-bearing polymers described in JP 7-36184 A, the phenolic hydroxy group-bearing acrylic resins described in JP 51-34711 A, the sulfonamide group-bearing acrylic resins described in JP 2-866 A, and urethane resins.

Conventional positive-type photosensitive compositions preferably contain as additives the compounds such as sensitivity regulators, print-out agents and dyes described in paragraphs [0024] to [0027] of JP 7-92660 A, and surfactants for enhancing coatability such as are described in paragraph [0031] of JP 7-92660 A.

Below the conventional positive-type photosensitive layer, it is advantageous to provide an intermediate layer similar to the intermediate layer which is preferably used in the case of the conventional negative-type photosensitive layer as above.

<Non-Treatment Type Photosensitive Compositions>

Illustrative examples of non-treatment type photosensitive compositions include thermoplastic polymer powder-based photosensitive compositions, microcapsule-based photosensitive compositions, and sulfonic acid-generating polymer-containing photosensitive compositions. All of these are heat-sensitive compositions containing a photothermal conversion substance. The photothermal conversion substance is preferably a dye of the same type as those which can be used in the above-described thermal positive-type photosensitive compositions.

Thermoplastic polymer powder-based photosensitive compositions are composed of a hydrophobic, heat-meltable finely divided polymer dispersed in a hydrophilic polymer matrix. In the thermoplastic polymer powder-based image recording layer, the fine particles of hydrophobic polymer melt under the influence of heat generated by light exposure and mutually fuse, forming hydrophobic regions which serve as the image areas.

The finely divided polymer is preferably one in which the particles melt and fuse together under the influence of heat. A finely divided polymer in which the individual particles have a hydrophilic surface, enabling them to disperse in a hydrophilic component such as fountain solution, is especially preferred. Preferred examples include the finely divided thermoplastic polymers described in Research Disclosure No. 33303 (January 1992), JP 9-123387 A, JP 9-131850 A, JP 9-171249 A, JP 9-171250 A and EP 931,647 A. Of these, polystyrene and polymethyl methacrylate are preferred. Illustrative examples of finely divided polymers having a hydrophilic surface include those in which the polymer itself is hydrophilic, and those in which the surfaces of the polymer particles have been rendered hydrophilic by adsorbing thereon a hydrophilic compound such as polyvinyl alcohol or polyethylene glycol.

The finely divided polymer preferably has reactive functional groups.

Preferred examples of microcapsule-type photosensitive compositions include those described in JP 2000-118160 A, and compositions like those described in JP 2001-277740 A in which a compound having thermally reactive functional groups is enclosed within microcapsules.

Illustrative examples of sulfonic acid-generating polymers that may be used in sulfonic acid generating polymer-containing photosensitive compositions include the polymers described in JP 10-282672 A that have sulfonate ester groups, disulfone groups or sec- or tert-sulfonamide groups in side chains.

Including a hydrophilic resin in a non-treatment type photosensitive composition not only provides a good on-press developability, it also enhances the film strength of the photosensitive layer itself. Preferred hydrophilic resins include resins having hydrophilic groups such as hydroxy, carboxy, hydroxyethyl, hydroxypropyl, amino, aminoethyl, aminopropyl or carboxymethyl groups; and hydrophilic binder resins of a sol-gel conversion-type.

A non-treatment type image recording layer can be developed on the press, and thus does not require a special development step. The methods described in detail in JP 2002-178655 A may be used as the method of forming a non-treatment type image recording layer and the associated platemaking and printing methods.

<Back Coat>

If necessary, the presensitized plate of the invention obtained by providing any of the various above image recording layers on a lithographic printing plate support obtained according to the invention may be provided on the rear side with a coat composed of an organic polymeric compound to prevent scuffing of the image recording layer when the presensitized plates are stacked on top of each other.

[Lithographic Platemaking Process]

A lithographic printing plate is prepared from the presensitized plate comprising a lithographic printing plate support obtained according to this invention by any of various treatment methods, depending on the type of image recording layer.

Illustrative examples of sources of actinic light that may be used for imagewise exposure include mercury vapor lamps, metal halide lamps, xenon lamps and chemical lamps. Examples of laser beams that may be used include those from helium-neon lasers (He—Ne lasers), argon lasers, krypton lasers, helium-cadmium lasers, KrF excimer lasers, semiconductor lasers, YAG lasers and YAG-SHG lasers.

Following the above exposure, if the image recording layer is of a thermal positive type, thermal negative type, conventional negative type, conventional positive type or photopolymer type, it is preferable to carry out development using a developer in order to prepare a lithographic printing plate.

The developer is preferably an alkaline developer, and more preferably an alkaline aqueous solution which is substantially free of organic solvent.

Developers which are substantially free of alkali metal silicates are also preferred. One example of a suitable method of development using a developer which is substantially free of alkali metal silicates is the method described in detail in JP 11-109637 A.

Developers which contain an alkali metal silicate may also be used.

EXAMPLES

Hereinafter, the present invention is described in detail with reference to non-limitative examples.

Examples 1 to 20 and Comparative Example 1

1. Production of Lithographic Printing Plate Support

The following aluminum plates 1 to 3 were subjected to the surface treatments as explained below to obtain lithographic printing plate supports.

<Aluminum Plates 1 to 3>

A melt was prepared from each of the aluminum alloys (Aluminum 1 to Aluminum 3) comprising various kinds of metal at proportions (wt %) as set forth in Table 1 below (with the balance being aluminum and inevitable impurities). The aluminum alloy melt was subjected to molten metal treatment and filtration, then was cast into a 500 mm thick, 1,200 mm wide ingot by a direct chill casting process. The ingot was scalped with a scalping machine, removing about 10 mm of material from the surface, then soaked and held at 550° C. for about 5 hours. When the temperature had fallen to 400° C., the ingot was rolled with a hot rolling mill to a thickness of 2.7 mm. The resulting rolled plate was further subjected to heat treatment at 500° C. in a continuous annealing furnace and then to cold rolling finish to have a thickness of 0.24 mm. After a process of defining the plate width to 1,030 mm, aluminum plates 1 to 3 were obtained. TABLE 1 Composition Si (wt %) Fe (wt %) Cu (wt %) Mn (wt %) Mg (wt %) Cr (wt %) Zn (wt %) Ti (wt %) Aluminum 1 0.080 0.300 0.001 0.001 0.000 0.001 0.003 0.021 Aluminum 2 0.076 0.270 0.023 0.001 0.000 0.001 0.003 0.021 Aluminum 3 0.278 0.413 0.201 0.892 0.783 0.022 0.122 0.034 <Surface Treatment>

The aluminum plates were successively subjected to the following surface treatments (a) to (k).

(a) Mechanical Graining Treatment

Volcanic foam was ground and classified to obtain a portion whose average particle size was 30 μm. The portion was used as an abrasive and added to water to prepare a suspension (specific gravity: 1.12) as an abrasive slurry. Using such an apparatus as schematically shown in FIG. 1, mechanical graining was carried out with rotating nylon roller brushes while feeding the slurry to the surface of the aluminum plate through spray lines.

The abrasive had a Mohs hardness of 5 and contained as abrasive components 73 wt % of SiO₂, 14 wt % of Al₂O₃, 1.2 wt % of Fe₂O₃, 1.34 wt % of CaO, 0.3 wt % of MgO, 2.6 wt % of K₂O, and 2.7 wt % of Na₂O.

The nylon brushes comprised the bristles No. 3 made of nylon 6.10 and having a length of 50 mm (before setting) and a diameter of 0.295 mm. In each brush, the nylon bristles were densely set in the holes formed in a stainless steel cylinder with a diameter of 300 mm. The brushes used were three in number.

Two support rollers (200 mm diameter) were situated below each nylon brush and spaced 300 mm apart. The direction in which the nylon brushes were rotated was the same as the direction of advance of the aluminum plate.

The indentation amount of the nylon brushes was modified by controlling the load on the driving motor rotating the brushes.

In the mechanical graining treatment, the flow rate of the abrasive slurry, the revolution number of the brushes, the speed of advance of the aluminum plate, and so forth were regulated appropriately so that the treated aluminum plate might have an average surface roughness R_(a) of 0.25 μm or more but less than 0.40 μm. Table 2 includes the average surface roughness R_(a) of the aluminum plate after the mechanical graining treatment.

In the case of Comparative Example 1, the abrasive slurry used was a suspension (specific gravity: 1.12) prepared by adding the abrasive composed of ground pumice with an average particle size of 60 μm to water, and the average surface roughness R_(a) of the treated surface was 0.7 μm.

The average surface roughness R_(a) of the aluminum plates was measured as follows: Two-dimensional roughness measurement was conducted using a stylus-type roughness tester (Surfcom 575 manufactured by Tokyo Seimitsu Co., Ltd.). For each plate, the average roughness R_(a) as defined in ISO 4287 was measured five times and the mean of the five measurements was found. The conditions of the two-dimensional roughness measurement were as follows.

<Measurement Conditions>

Cutoff value, 0.8 mm; slope correction, FLAT-ML; measurement length, 3 mm; vertical magnification, 10,000×; scan rate, 0.3 mm/sec; stylus tip diameter, 2 μm.

(b) Etching in Aqueous Alkali Solution (First Alkali Etching Treatment)

Etching was carried out by spraying the aluminum plates with an aqueous solution having a sodium hydroxide concentration of 370 g/L, an aluminum ion concentration of 100 g/L and a temperature of 60° C. from a spray line. Table 2 includes the etching amount for the aluminum plate surface to be subsequently subjected to the first hydrochloric acid electrolysis. The solution was removed from the plates with nip rollers and, after the rinsing treatment as explained below, the rinse water was also removed with nip rollers. The rinsing treatment was such that an apparatus for rinsing with a free-falling curtain of water was initially used to carry out rinsing and then a spray line having a plurality of spray tips located at an interval of 80 mm, each discharging a fanned-out spray of water, for a rinsing for 5 seconds.

(c) Desmutting in Aqueous Acidic Solution (First Desmutting Treatment)

Next, desmutting treatment was performed. The aqueous acidic solution used in the desmutting treatment was the wastewater (170 g/L aqueous solution of sulfuric acid with 5 g/L of aluminum ions dissolved therein) generated in the anodizing treatment step. Desmutting was carried out for 5 seconds by spaying the aluminum plates with the aqueous acidic solution as above (temperature: 50° C.) from a spray line.

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

(d) First Electrochemical Graining with Alternating Current in Aqueous Acidic Solution (First Hydrochloric Acid Electrolysis)

The hydrochloric acid concentration, aluminum ion concentration, sulfuric acid concentration and temperature of the electrolyte solutions used in this treatment were as set forth in Table 2. The aluminum ion concentration was modified by dissolving aluminum chloride in the aqueous solutions having hydrochloric acid concentrations as shown in Table 2.

Electrochemical graining treatment was performed by using a power supply generating an alternating current of any waveform, which regulates electric current through inverter control with an IGBT device. The waveform of the AC power supply waves generated was a sinusoidal one as shown in FIG. 6A and the sinusoidal wave alternating current had a frequency of 60 Hz and a duty ratio (ta/T) of 0.5.

Carbon electrodes were used as the counter electrodes. For the auxiliary anodes, ferrite was used. An electrolytic cell as shown in FIG. 4 was used as the sole electrolytic cell.

The current density at alternating current peaks during the anodic reaction on the aluminum plate and the amount of electricity (total amount of electricity during the anodic reaction on the aluminum plate) were as shown in Table 2. The ratio between the total amounts of electricity during the anodic reaction and the cathodic reaction on the aluminum plate was 0.95. The current from the power supply was diverted to the auxiliary anodes by 5%. The relative velocity between the aluminum plate and the electrolyte solution was 1 m/sec on average in the cell.

The average surface roughness R_(a) after the first hydrochloric acid electrolysis was measured on the aluminum plates from which the generated smut components had been removed by immersing the plates in a 300 g/L aqueous solution of sulfuric acid for 60 seconds. Processes and conditions for the measurement were the same as for the average surface roughness R_(a) measurement in the above (a).

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

(e) Etching in Aqueous Alkali Solution (Second Alkali Etching Treatment)

Etching was carried out by spraying the aluminum plates with an aqueous solution having a sodium hydroxide concentration of 50 g/L, an aluminum ion concentration of 5 g/L and a temperature of 35° C. from a spray line. Table 2 includes the etching amount for the aluminum plate surface to be subsequently subjected to the second hydrochloric acid electrolysis.

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

The second alkali etching treatment was not performed in Example 20, which is denoted by “-” in Table 2.

(f) Desmutting in Aqueous Acidic Solution (Second Desmutting Treatment)

Next, desmutting treatment was performed. The aqueous acidic solution used in the desmutting treatment was the wastewater (170 g/L aqueous solution of sulfuric acid with 5 g/L of aluminum ions dissolved therein) generated in the anodizing treatment step. Desmutting was carried out for 5 seconds by spaying the aluminum plates with the aqueous acidic solution as above (temperature: 50° C.) from a spray line.

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

The second desmutting treatment was not performed in Example 20.

(g) Second Electrochemical Graining with Alternating Current in Aqueous Acidic Solution (Second Hydrochloric Acid Electrolysis)

The hydrochloric acid concentration, aluminum ion concentration, sulfuric acid concentration and temperature of the electrolyte solutions used in this treatment were as set forth in Table 2. The aluminum ion concentration was modified by dissolving aluminum chloride in the aqueous solutions having hydrochloric acid concentrations as shown in Table 2.

Electrochemical graining treatment was performed by using a power supply generating an alternating current of any waveform, which regulates electric current through inverter control with an IGBT device. The waveform of the AC power supply waves generated was a sinusoidal one as shown in FIG. 6A or a trapezoidal one as shown in FIG. 6B and the trapezoidal wave alternating current had a frequency of 60 Hz, a time TP of 0.8 msec, in which the current value changed from zero to a peak, and a duty ratio (ta/T) of 0.5.

Carbon electrodes were used as the counter electrodes. For the auxiliary anodes, ferrite was used. An electrolytic cell as shown in FIG. 4 was used as the sole electrolytic cell.

The current density at alternating current peaks during the anodic reaction on the aluminum plate and the amount of electricity (total amount of electricity during the anodic reaction on the aluminum plate) were as shown in Table 2. The ratio between the total amounts of electricity during the anodic reaction and the cathodic reaction on the aluminum plate was 0.95. The current from the power supply was diverted to the auxiliary anodes by 5%. The relative velocity between the aluminum plate and the electrolyte solution was 1 m/sec on average in the cell.

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

The second hydrochloric acid electrolysis was not performed in Example 20, which is denoted by “-” in Table 2.

(h) Etching in Aqueous Alkali Solution (Third Alkali Etching Treatment)

Etching was carried out by spraying the aluminum plates with an aqueous solution having a sodium hydroxide concentration of 50 g/L, an aluminum ion concentration of 5 g/L and a temperature of 35° C. from a spray line. Table 2 includes the etching amount for the aluminum plate surface subjected to the second hydrochloric acid electrolysis.

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

(i) Desmutting in Aqueous Acidic Solution (Third Desmutting Treatment)

Next, desmutting treatment was performed. The aqueous acidic solution used in the desmutting treatment was the wastewater (170 g/L aqueous solution of sulfuric acid with 5 g/L of aluminum ions dissolved therein) generated in the anodizing treatment step. Desmutting was carried out for 5 seconds by spaying the aluminum plates with the aqueous acidic solution as above (temperature: 50° C.) from a spray line.

The solution was removed from the plates with nip rollers. No rinsing treatment was performed prior to the subsequent anodizing treatment.

(j) Anodizing Treatment

Anodizing treatment was performed using an anodizing apparatus as shown in FIG. 5.

The electrolyte solution used was prepared by dissolving aluminum sulfate in a 170 g/L aqueous sulfuric acid solution to an aluminum ion concentration of 5 g/L, and had a temperature of 50° C. Anodizing treatment was carried out in such a way that the average current density during the anodic reaction of the the anodized layer was 2.7 g/m².

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers.

(k) Hydrophilizing Treatment

Hydrophilizing treatment was carried out by immersing the aluminum plates in a 1.0 wt % solution of sodium silicate in water (solution temperature: 20° C.) for 10 seconds. The amount of silicon on the surface of each aluminum plate, as measured by a fluorescent x-ray analyzer, was 3.5 mg/m².

The solution was removed from the plates with nip rollers. Rinsing treatment was then performed using a spray line which is similar in structure to that used for the rinsing treatment in the above (b), and the rinse water was removed from the plates with nip rollers. After that, the aluminum plates were dried by blowing 90° C. air thereon for 10 seconds, thereby giving the lithographic printing plate supports. TABLE 2 R_(a) after First hydrochloric acid electrolysis R_(a) after mechanical Etching amount Hydrochloric Solution first hydro- Alumi- graining in first acid concen- Aluminum ion Sulfuric acid tempera- Current Amount of chloric acid num treatment alkali etching tration concentration concentration ture density electricity electrolysis plate (μm) (g/m²) (g/L) (g/L) (g/L) (° C.) (A/dm²) (C/dm²) (μm) Example 1 1 0.28 3 7.5 4.5 0 35 60 350 0.43 Example 2 1 0.30 3 7.5 4.5 0 35 60 350 0.45 Example 3 1 0.35 3 7.5 4.5 0 35 60 300 0.45 Example 4 1 0.35 3 7.5 4.5 0 35 60 350 0.48 Example 5 2 0.35 3 7.5 4.5 0 35 60 350 0.48 Example 6 1 0.35 3 7.5 4.5 0 35 60 350 0.48 Example 7 1 0.35 3 7.5 4.5 0 35 60 350 0.48 Example 8 1 0.35 3 7.5 4.5 0 35 60 350 0.48 Example 9 1 0.35 3 7.5 4.5 0 35 60 400 0.50 Example 10 1 0.35 5 7.5 4.5 0 35 60 350 0.48 Example 11 1 0.35 10 7.5 4.5 0 35 60 350 0.48 Example 12 1 0.40 3 7.5 4.5 0 35 60 350 0.52 Example 13 1 0.35 3 15.0 12.0 2 30 80 350 0.45 Example 14 1 0.35 3 15.0 12.0 3 30 80 350 0.45 Example 15 1 0.35 3 15.0 12.0 4 30 80 350 0.45 Example 16 1 0.35 3 15.0 12.0 3 30 80 350 0.45 Example 17 2 0.35 3 15.0 12.0 3 30 80 350 0.45 Example 18 3 0.35 3 15.0 12.0 3 30 80 350 0.45 Example 19 1 0.35 5 7.5 4.5 0 35 60 350 0.48 Example 20 1 0.35 3 7.5 4.5 0 35 60 350 0.48 Comparative 1 0.70 3 7.5 4.5 0 35 60 350 0.80 Example 1 Second hydrochloric acid electrolysis Etching amount Power Hydrochloric Etching amount in second supply acid concen- Aluminum ion Sulfuric acid Solution Current Amount of in third alkali etching wave- tration concentration concentration temperature density electricity alkali etching (g/m²) form (g/L) (g/L) (g/L) (° C.) (A/dm²) (C/dm²) (g/m²) Example 1 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 2 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 3 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 4 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 5 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 6 0.2 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 7 0.2 Trapezoidal 5 4.5 0 35 50 65 0.2 Example 8 0.7 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 9 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 10 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 11 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 12 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 13 0.5 Trapezoidal 7.5 4.5 0 35 50 65 0.1 Example 14 0.5 Trapezoidal 7.5 4.5 0 35 50 65 0.1 Example 15 0.5 Trapezoidal 7.5 4.5 0 35 50 65 0.1 Example 16 0.5 Trapezoidal 7.5 4.5 3 35 50 65 0.1 Example 17 0.5 Trapezoidal 7.5 4.5 0 35 50 65 0.1 Example 18 0.5 Trapezoidal 7.5 4.5 0 35 50 65 0.1 Example 19 0.5 Sinusoidal 5 4.5 0 35 50 65 0.1 Example 20 — — — — — — — — 0.1 Comparative 0.5 Trapezoidal 5 4.5 0 35 50 65 0.1 Example 1 2. Evaluation of Lithographic Printing Plate Support

The surface profile of the lithographic printing plate supports obtained in Examples 1 to 20 was examined under a scanning electron microscope (JSM-5500 manufactured by JEOL, Ltd.; the same applies below) at a magnification of 50,000×, whereupon fine recesses with a diameter of 0.1 to 0.2 μm were found to have uniformly and densely been formed on the surface of each support. In addition, it was found upon the examination under the scanning electron microscope at a magnification of 2,000× that recesses with a diameter of 1 to 5 μm had been formed on the surfaces of the lithographic printing plate supports. The fine recesses with a diameter of 0.1 to 0.2 μm were superimposed on the recesses with a diameter of 1 to 5 μm.

On the other hand, the surface profile of the lithographic printing plate support obtained in Comparative Example 1 was also examined in the same manner, and fine recesses with a diameter of 0.1 to 0.2 μm and recesses with a diameter of 1 to 5 μm were found to have been formed on the surface of the support, part of the recesses being formed rather deep.

3. Production of Presensitized Plate

Presensitized plates for lithographic printing were fabricated by providing a thermal positive-type image recording layer in the manner described below on the respective lithographic printing plate supports obtained as above. Before providing the image recording layer, an undercoat was formed on the support as follows.

An undercoating solution of the composition indicated below was applied onto the lithographic printing plate support and dried at 80° C. for 15 seconds, thereby forming an undercoat layer. The weight of the undercoat layer after drying was 15 mg/m².

<Composition of Undercoating Solution> Polymeric compound of the following formula 0.3 g

Methanol 100 g Water 1 g

Next, a heat-sensitive layer-forming coating solution of the following composition was prepared and applied onto the undercoated lithographic printing plate support to a coating weight (heat-sensitive layer weight) after drying of 1.8 g/m². As a result of subsequent drying, a heat-sensitive layer (thermal positive-type image recording layer) was formed and a presensitized plate was thus obtained.

<Composition of Heat-Sensitive Layer-Forming Coating Solution> Novolak resin (m-cresol/p-cresol = 60/40; weight-average 0.90 g molecular weight, 7,000; unreacted cresol content, 0.5 wt %) Ethyl methacrylate/isobutyl methacrylate/methacrylic acid 0.10 g copolymer (molar ratio, 35/35/30) Cyanine dye A of the following formula 0.1 g

Tetrahydrophthalic anhydride 0.05 g p-Toluenesulfonic acid 0.002 g Ethyl violet in which counterion was 6-hydroxy-β- 0.02 g naphthalenesulfonic acid Fluorochemical surfactant (Megaface F-780F, product of 0.0045 g Dainippon Ink and Chemicals, Inc.; 30 wt % solids) (as solids) Fluorochemical surfactant (Megaface F-781F, product of 0.035 g Dainippon Ink and Chemicals, Inc.; 100 wt % solids) Methyl ethyl ketone 12 g 4. Evaluation of Presensitized Plate

The sensitivity of the resulting presensitized plates as well as the scumming resistance, press life and cleaner resistance (resistance to chemicals) of the lithographic printing plates prepared from them were evaluated. Evaluation methods were as follows.

(1) Sensitivity

On Trendsetter manufactured by Creo, the presensitized plates were subjected to the image forming at a drum rotation speed of 150 rpm with a laser output changed by 1 W.

The presensitized plates were then developed with PS Processor 940H manufactured by Fuji Photo Film Co., Ltd. that was charged with an alkaline developer of the following composition so as to obtain lithographic printing plates. During the development, the temperature of the developer was kept to 30° C. and the developing time was set to 20 seconds.

<Composition of Alkaline Developer> D-sorbitol 2.5 wt % Sodium hydroxide 0.85 wt % Polyethylene glycol lauryl ether (weight-average 0.5 wt % molecular weight: 1,000) Water 96.15 wt %

The regions on the printing plates in which image forming was carried out with various laser outputs were visually inspected and the minimum laser output required for the complete removal of the image recording layer was assumed to be the sensitivity. A smaller laser output suggests a higher sensitivity, namely, a higher developability. The evaluation results are shown in Table 3 below. In the table, the letter A means that the minimum laser output was less than 5 W, the letter B means that the minimum laser output was 5 W or more but less than 10 W, and the letter C means that the minimum laser output was 10 W or more.

(2) Scumming Resistance

With the lithographic printing plates obtained as above, printing was carried out on a Mitsubishi DAIYA F2 printing press (manufactured by Mitsubishi Heavy Industries, Ltd.) using DIC-GEOS (s) magenta ink. The scumming resistance of each printing plate was evaluated by visually inspecting the blanket for stains after ten thousand printed sheets had been made from the relevant plate.

Results are shown in Table 3. In the table, the letter A means that the blanket had almost no stains, the letter B means that the blanket had tolerable stains, and the letter C means that the blanket was certainly stained and the printed sheets underwent evident scumming.

(3) Press Life

Printing was carried out with the obtained lithographic printing plates on a Lithrone printing press manufactured by Komori Corporation using DIC-GEOS(N) black ink, a product of Dainippon Ink and Chemicals, Inc. The press life of each printing plate was evaluated based on the number of the printed sheets which had already been made from the relevant plate at the time when the decrease in density of a solid image became visually recognizable. Naturally, a larger number implied a better press life. Results are shown in Table 3. In the table, the letter A means that the number was 30,000 or more and the letter B means that the number was 20,000 or more but less than 30,000.

(4) Cleaner Resistance (Resistance to Chemicals)

Printing was carried out in the same manner as in the above (3), evaluation of the press life, except that Multi-cleaner manufactured by Fuji Photo Film Co., Ltd was applied to the surface of the image recording layer for one minute every time 5,000 printed sheets had been made, and then wiped off with water. The cleaner resistance was evaluated based on the number of the printed sheets which had already been made from the relevant printing plate at the time when the ink density (reflection density) was reduced by 0.1 from the value upon start of printing.

Results are shown in Table 3. In the table, the letter A means that the number was 10,000 or more, the letters A-B mean that the number was 6,000 or more but less than 10,000, and the letter B means that the number was 3,000 or more but less than 6,000.

As is evident from Table 3, every presensitized plate using any of the lithographic printing plate supports obtained by the method of manufacturing a lithographic printing plate support according to the present invention (Examples 1 to 20) had a high sensitivity as well as an excellent scumming resistance, good press life and further a high cleaner resistance when made into a lithographic printing plate.

On the other hand, the presensitized plate using the lithographic printing plate support of Comparative Example 1 which had an average surface roughness R_(a) of 0.70 μm after the mechanical graining treatment by brush graining did not have an adequate sensitivity or scumming resistance.

Moreover, the presensitized plates using the lithographic printing plate supports obtained by the method of manufacturing a lithographic printing plate support according to the present invention (Examples 1 to 20), in particular those using the lithographic printing plate supports obtained in Examples 13 to 18 in which the hydrochloric acid concentration was increased in the first and second hydrochloric acid electrolyses, were all found to be excellent in cleaner resistance. TABLE 3 Printing performance Scumming Cleaner Sensitivity resistance Press life resistance Example 1 A A B B Example 2 A A A A Example 3 A A A A Example 4 A A A A Example 5 A A A A Example 6 A A A A Example 7 A A A A Example 8 A A A A Example 9 A B A A Example 10 A A A A Example 11 A A B B Example 12 B A A A Example 13 A A A A Example 14 A A A A Example 15 A A A A Example 16 A A A A Example 17 A A A A Example 18 A A A A Example 19 A A A A Example 20 B B B B Comparative C C B B Example 1 

1. A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least: a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, and an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm, with the treatments being performed in this order, so as to obtain a lithographic printing plate support.
 2. A method of manufacturing a lithographic printing plate support, comprising a step of subjecting an aluminum plate to at least: a mechanical graining treatment using a brush and a slurry containing an abrasive to carry out mechanical graining such that the average surface roughness R_(a) is 0.25 μm or more but less than 0.40 μm, an first etching treatment in an aqueous alkali solution, an electrochemical graining treatment for carrying out electrochemical graining in an aqueous solution containing hydrochloric acid such that the average surface roughness R_(a) is 0.40 to 0.55 μm, an second etching treatment in an aqueous alkali solution, an electrochemical graining treatment in an aqueous solution containing hydrochloric acid, an third etching treatment in an aqueous alkali solution, and an anodizing treatment, with the treatments being performed in this order, so as to obtain a lithographic printing plate support.
 3. The method of manufacturing a lithographic printing plate support according to claim 2, wherein a desmutting treatment is performed subsequent to at least one of the first etching treatment in an aqueous alkali solution, the second etching treatment in an aqueous alkali solution and the third etching treatment in an aqueous alkali solution. 